build.sh: Add --boot option
build.sh: Add --boot option

It allows build and boot IBL using fastboot boot without flashing it to storage

jsr-d10/android_bootable_bootloader_lk,jsr-d10/android_bootable_bootloader_lk,jsr-d10/android_bootable_bootloader_lk,jsr-d10/android_bootable_bootloader_lk,jsr-d10/android_bootable_bootloader_lk