generate multiple boot.img files in aosp_arm64

Generate boot.img variants with different schemes for kernel compression
(gzip, lz4, none).

The boot image is removed from vbmeta for aosp_arm64 since it is
not possible currently to store the hashes of multiple variants of a
particular image. The GKI will be verified via VTS anyway.

Also remove some emulator-specific stuff from aosp_arm64.

Bug: 151094943
Change-Id: I465ea6c98d52e839284d51b246203f6b8dfb5566
diff --git a/core/Makefile b/core/Makefile
index a158c9d..401696d 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -3510,8 +3510,12 @@
 endef
 
 ifdef INSTALLED_BOOTIMAGE_TARGET
+# multiple hashes for an image are not yet supported, fortunately this
+# only arises for GKI where the boot descriptor can be left out
+ifeq ($(strip $(BOARD_KERNEL_BINARIES)),)
 $(eval $(call check-and-set-avb-args,boot))
 endif
+endif
 
 ifdef INSTALLED_VENDOR_BOOTIMAGE_TARGET
 $(eval $(call check-and-set-avb-args,vendor_boot))