google boards: auto-select CACHE_ROM

Automatically select CACHE_ROM for all Google boards.
Tested by generating a config for the link board. CACHE_ROM
was selected and was unable to unselect it using
'make oldconfig'.

Change-Id: I8e34207e3929a020bb0280657f95ba7a000ad024
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/2963
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/google/Kconfig

@@ -18,6 +18,11 @@
 ##
 if VENDOR_GOOGLE
 
+# Auto select common options
+config VENDOR_SPECIFIC_OPTIONS
+	def_bool y
+	select CACHE_ROM
+
 choice
 	prompt "Mainboard model"