Resize boot_16k.img properly

Bootloaders often assume boot partition to be 64MB in size. Correctly
size boot_16k.img so that bootloader can verify the AVB footers.

Test: th
Bug: 293313353
Change-Id: I322277b10e99a41c9a262ff76e2f29c3ed16fec0
diff --git a/core/Makefile b/core/Makefile
index 9be879d..504363d 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1098,6 +1098,8 @@
 
 BUILT_BOOTIMAGE_16K_TARGET := $(PRODUCT_OUT)/boot_16k.img
 
+BOARD_KERNEL_16K_BOOTIMAGE_PARTITION_SIZE := $(BOARD_BOOTIMAGE_PARTITION_SIZE)
+
 $(BUILT_BOOTIMAGE_16K_TARGET): $(MKBOOTIMG) $(AVBTOOL) $(INTERNAL_BOOTIMAGE_FILES) $(BOARD_AVB_BOOT_KEY_PATH) $(INTERNAL_GKI_CERTIFICATE_DEPS)
 	$(call pretty,"Target boot 16k image: $@")
 	$(call build_boot_from_kernel_avb_enabled,$@,$(BUILT_KERNEL_16K_TARGET))