drivers/mrc_cache: Always generate an FMAP region

This automatically generates an FMAP region for the MRC_CACHE driver
which is easier to handle than a cbfsfile.

Adds some spaces and more comments to Makefile.inc to improve
readability.

Tested on Thinkpad x200 with some proof of concept patches.

Change-Id: Iaaca36b1123b094ec1bbe5df4fb25660919173ca
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/23150
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

util/cbfstool/default-x86.fmd

@@ -11,6 +11,7 @@ FLASH@##ROM_BASE## ##ROM_SIZE## {
 	BIOS@##BIOS_BASE## ##BIOS_SIZE## {
 		FMAP@##FMAP_BASE## ##FMAP_SIZE##
 		##CONSOLE_ENTRY##
+		##MRC_CACHE_ENTRY##
 		COREBOOT(CBFS)@##CBFS_BASE## ##CBFS_SIZE##
 	}
 }

util/cbfstool/default.fmd

@@ -14,6 +14,7 @@ FLASH@##ROM_BASE## ##ROM_SIZE## {
 		BOOTBLOCK 128K
 		FMAP@##FMAP_BASE## ##FMAP_SIZE##
 		##CONSOLE_ENTRY##
+		##MRC_CACHE_ENTRY##
 		COREBOOT(CBFS)@##CBFS_BASE## ##CBFS_SIZE##
 	}
 }