libfdt: Add more documentation (patch the seventh)
libfdt: Add more documentation (patch the seventh)

This patch adds more documenting comments to libfdt.h.  Specifically,
these document the read/write functions (not including fdt_open_into()
and fdt_pack(), for now).

Signed-off-by: David Gibson <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@gibson.dropbear.id.au>

Foxda-Tech/argo8-bootable-bootloader-lk,utilite2/lk,Redmi-dev/android_bootable_lk,Foxda-Tech/polaris-bootable-bootloader-lk,oubeichen/lk-v500,t2m-foxfone/kernel_lk,jbott/lk_gee,Foxda-Tech/argo8-bootable-bootloader-lk,RonGokhale/android_lk_bootloader,idor/dk50-bootable_bootloader_lk,lg-devs/g2-bootloader,thornbirdblue/codeaurora_lk,chirayudesai/android_bootable_bootloader_lk,jsr-d10/android_bootable_bootloader_lk,pichina/lk,M1cha/lktris,Foxda-Tech/polaris-bootable-bootloader-lk,idor/dk50-bootable_bootloader_lk,t2m-foxfone/android_kernel_lk,efidroid/lk,Foxda-Tech/argo8-bootable-bootloader-lk,thornbirdblue/codeaurora_lk,detule/lk-g2-spr,zhuotong/mi2_lk_NoEmmc,CanarySolutions/little-kernel,DooMLoRD/android_bootable_bootloader_lk,detule/lk-g2-spr,t2m-foxfone/android_kernel_lk,CanarySolutions/little-kernel,RonGokhale/android_lk_bootloader,zhuotong/mi2_lk_NoEmmc,Foxda-Tech/argo8-bootable-bootloader-lk,utilite2/lk,M1cha/android_bootable_bootloader_lk,t2m-foxfone/kernel_lk,jsr-d10/android_bootable_bootloader_lk,efidroid/lk,M1cha/mi2_lk,lg-devs/g2-bootloader,M1cha/lktris,pichina/lk,thornbirdblue/codeaurora_lk,lg-devs/g2-bootloader,MiCode/mi2_lk,Redmi-dev/android_bootable_lk,idor/dk50-bootable_bootloader_lk,DooMLoRD/android_bootable_bootloader_lk,M1cha/mi2_lk,zhuotong/mi2_lk_NoEmmc,idor/dk50-bootable_bootloader_lk,lg-devs/g2-bootloader,hanjae/lumiab0,M1cha/mi2_lk,MiCode/mi2_lk,t2m-foxfone/android_kernel_lk,mozilla-b2g/fairphone2_kernel_lk,jbott/lk_gee,Blefish/android_bootable_bootloader_lk,utilite2/lk,mozilla-b2g/fairphone2_kernel_lk,mozilla-b2g/kernel_lk,chirayudesai/android_bootable_bootloader_lk,Blefish/android_bootable_bootloader_lk,jsr-d9/android_kernel_lk,Foxda-Tech/argo8-bootable-bootloader-lk,Foxda-Tech/polaris-bootable-bootloader-lk,Foxda-Tech/polaris-bootable-bootloader-lk,MiCode/mi2_lk,mozilla-b2g/kernel_lk,efidroid/lk,mozilla-b2g/fairphone2_kernel_lk,MiCode/mi2_lk,lg-devs/g2-bootloader,CanarySolutions/little-kernel,jsr-d9/android_kernel_lk,jsr-d9/android_kernel_lk,t2m-foxfone/kernel_lk,jsr-d9/android_kernel_lk,idor/dk50-bootable_bootloader_lk,efidroid/lk,zhuotong/mi2_lk_NoEmmc,RonGokhale/android_lk_bootloader,M1cha/android_bootable_bootloader_lk,oubeichen/lk-v500,M1cha/android_bootable_bootloader_lk,jsr-d10/android_bootable_bootloader_lk,DooMLoRD/android_bootable_bootloader_lk,M1cha/android_bootable_bootloader_lk,chirayudesai/android_bootable_bootloader_lk,utilite2/lk,efidroid/lk,DooMLoRD/android_bootable_bootloader_lk,mozilla-b2g/kernel_lk,Redmi-dev/android_bootable_lk,detule/lk-g2-spr,Redmi-dev/android_bootable_lk,M1cha/android_bootable_bootloader_lk,M1cha/lktris,mozilla-b2g/kernel_lk,CanarySolutions/little-kernel,t2m-foxfone/android_kernel_lk,M1cha/lktris,chirayudesai/android_bootable_bootloader_lk,Blefish/android_bootable_bootloader_lk,M1cha/mi2_lk,chirayudesai/android_bootable_bootloader_lk,oubeichen/lk-v500,Redmi-dev/android_bootable_lk,jsr-d9/android_kernel_lk,jsr-d10/android_bootable_bootloader_lk,thornbirdblue/codeaurora_lk,Foxda-Tech/polaris-bootable-bootloader-lk,hanjae/lumiab0,oubeichen/lk-v500,M1cha/android_bootable_bootloader_lk,utilite2/lk,RonGokhale/android_lk_bootloader,Blefish/android_bootable_bootloader_lk,pichina/lk,Blefish/android_bootable_bootloader_lk,t2m-foxfone/android_kernel_lk,M1cha/mi2_lk,zhuotong/mi2_lk_NoEmmc,hanjae/lumiab0,jsr-d10/android_bootable_bootloader_lk,M1cha/lktris,DooMLoRD/android_bootable_bootloader_lk,pichina/lk,hanjae/lumiab0,detule/lk-g2-spr,mozilla-b2g/fairphone2_kernel_lk,t2m-foxfone/kernel_lk,oubeichen/lk-v500,pichina/lk,t2m-foxfone/kernel_lk,thornbirdblue/codeaurora_lk,mozilla-b2g/fairphone2_kernel_lk,jbott/lk_gee,jbott/lk_gee,RonGokhale/android_lk_bootloader,hanjae/lumiab0,jbott/lk_gee,detule/lk-g2-spr,mozilla-b2g/kernel_lk,MiCode/mi2_lk,CanarySolutions/little-kernel