soc/amd/pi: Use -Wno-pragma-pack

Agesa headers extensively use and override pragma pack which fails to
compile with clang.

Change-Id: Ib234be536388f41d63c2d26cac4c35881af25930
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63054
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/soc/amd/common/pi/Makefile.inc

@@ -16,4 +16,7 @@ ramstage-y += image.c
 ramstage-y += refcode_loader.c
 ramstage-y += s3_resume.c
 
+CFLAGS_x86_32 += -Wno-pragma-pack
+CFLAGS_x86_64 += -Wno-pragma-pack
+
 endif # CONFIG_SOC_AMD_PI