Build GKI APEX from $(PRODUCT_OUT)/boot*.img

Test: on CF build boot_5.4-android12-0 and inspect output
Test: on aosp_arm64 build boot-5.4_5.4-android12-0 and inspect output

Bug: 161563386
Change-Id: I74988d9d78f7074e331ef46cc0aee52c3201ab8a
7 files changed