option: Introduce `CMOS_LAYOUT_FILE` Kconfig symbol

Mainboards with variants may not always use the same cmos.layout file.
Turn the hardcoded path into a Kconfig symbol to allow changing it.

Tested with BUILD_TIMELESS=1: Without including the config file in the
coreboot.rom and with `USE_OPTION_TABLE` selected, building for the Asus
P8H61-M PRO produces an identical coreboot image.

Change-Id: I4cc622dcb70855c06cb8a816c34406f8421180df
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/54366
Reviewed-by: Martin Roth <martinroth@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/Makefile.inc b/Makefile.inc
index da54e3b..eb505e5 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -302,9 +302,9 @@
 # arg1: source file
 # arg2: binary file name
 cbfs-files-processor-nvramtool= \
-	$(eval $(2): $(1) $(src)/mainboard/$(MAINBOARDDIR)/cmos.layout | $(objutil)/nvramtool/nvramtool ; \
+	$(eval $(2): $(1) $(top)/$(call strip_quotes,$(CONFIG_CMOS_LAYOUT_FILE)) | $(objutil)/nvramtool/nvramtool ; \
 		printf "    CREATE     $(2) (from $(1))\n"; \
-		$(objutil)/nvramtool/nvramtool -y $(src)/mainboard/$(MAINBOARDDIR)/cmos.layout -D $(2).tmp -p $(1) && \
+		$(objutil)/nvramtool/nvramtool -y $(top)/$(call strip_quotes,$(CONFIG_CMOS_LAYOUT_FILE)) -D $(2).tmp -p $(1) && \
 		mv $(2).tmp $(2))
 
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