libpayload: Add -Wno-address-of-packed-member for ARCH_MOCK

When compiling libpayload using x86_64 toolchain for ARCH_MOCK compiler
reports an error about gerring address of packed member. Until now it
had to be disabled by passing -Wno-address-of-packed-member to
EXTRA_CFLAGS. This patch disables this warning.

Change-Id: I9a948fabe66f7297632ecaca8ec1bfa5c842b750
Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60169
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

payloads/libpayload/arch/mock/Makefile.inc

@@ -5,3 +5,5 @@ head.o-y += head.c
 libc-y += virtual.c
 
 libcbfs-$(CONFIG_LP_CBFS) += mock_media.c
+
+CFLAGS += -Wno-address-of-packed-member