Only build system_other.avbpubkey when AVB is enabled

/product/etc/security/avb/system_other.avbpubkey is only needed
when BOARD_AVB_ENABLE is true. This fixes the build error of
Marlin/Sailfish.

Bug: 123611926
Bug: 129029207
Test: make
Change-Id: I73f948d84f91cd6fbe49a2de7bf12e46eebe6ede
diff --git a/core/Makefile b/core/Makefile
index a0aa94f..69c75ca 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -732,8 +732,10 @@
 # -----------------------------------------------------------------
 # build /product/etc/security/avb/system_other.avbpubkey if needed
 ifdef BUILDING_SYSTEM_OTHER_IMAGE
+ifeq ($(BOARD_AVB_ENABLE),true)
 INSTALLED_PRODUCT_SYSTEM_OTHER_AVBKEY_TARGET := $(TARGET_OUT_PRODUCT_ETC)/security/avb/system_other.avbpubkey
 ALL_DEFAULT_INSTALLED_MODULES += $(INSTALLED_PRODUCT_SYSTEM_OTHER_AVBKEY_TARGET)
+endif # BOARD_AVB_ENABLE
 endif # BUILDING_SYSTEM_OTHER_IMAGE
 
 # -----------------------------------------------------------------