vboot: Exclude platform specific files from RW cbfs

Add a Kconfig option to allow platforms to exclude specific files
from being copied from RO into RW sections.

BUG=b:65484600
TEST=Exclude apu/amdfw from the RW cbfs sections

Change-Id: I7723b63392c1620b75ceb6d8e25fe1ce2c75cf18
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/21899
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/vboot/Kconfig

@@ -221,6 +221,13 @@ config VBOOT_FWID_VERSION
 	  This is the second part of the FWID written to various regions of a
 	  vboot firmware image to identify its version.
 
+config RO_REGION_ONLY
+	string "Additional files that should not be copied to RW"
+	default ""
+	help
+	  Add a space delimited list of filenames that should only be in the
+	  RO section.
+
 menu "GBB configuration"
 
 config GBB_HWID

src/vboot/Makefile.inc

@@ -152,6 +152,7 @@ regions-for-file = $(subst $(spc),$(comma),$(sort \
 		font.bin \
 		vbgfx.bin \
 		rmu.bin \
+		$(call strip_quotes,$(CONFIG_RO_REGION_ONLY)) \
 		,$(1)),COREBOOT,COREBOOT FW_MAIN_A FW_MAIN_B)))
 
 CONFIG_GBB_HWID := $(call strip_quotes,$(CONFIG_GBB_HWID))