Adding BOARD_BUILD_GKI_BOOT_IMAGE_WITHOUT_RAMDISK

GKI targets, e.g., `gki_arm64` or `gki_x86_64` have only
boot-*.img files without a ramdisk. It has no other images,
e.g., init_boot.img, system.img, etc.

The current build system assumes that the ramdisk is either
in a boot.img or in a init_boot.img, which is not true for
those GKI targets. Adding a new flag to support building
boot-*.img without a ramdisk while not building an init_boot.img.

Bug: 220834917
Test: build and `unpack_bootimg`
Change-Id: I789343c3e3d9ff0c36c0e19680a9792bd31a1c9f

tools/releasetools/common.py

@@ -1782,6 +1782,9 @@ def HasRamdisk(partition_name, info_dict=None):
   if info_dict.get("recovery_as_boot") == "true":
     return True  # the recovery-as-boot boot.img has a RECOVERY ramdisk.
 
+  if info_dict.get("gki_boot_image_without_ramdisk") == "true":
+    return False  # A GKI boot.img has no ramdisk since Android-13.
+
   if info_dict.get("system_root_image") == "true":
     # The ramdisk content is merged into the system.img, so there is NO
     # ramdisk in the boot.img or boot-<kernel version>.img.