build: Allow target override from TARGET_PRODUCT
build: Allow target override from TARGET_PRODUCT

If defined, use $TARGET_BOOTLOADER_PLATFORM_OVERRIDE as
LK build target instead of $TARGET_PRODUCT.

Change-Id: I1444c261a7b8fd8202ace74c10c8dce097ea4263

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