link: select write-combining memory for graphics

Auto-select marking the graphics memory as write-combining.

Change-Id: I0b913f0b318bf57275643d3cfb5bc54ca8a005f5
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/2982
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/google/link/Kconfig

@@ -20,6 +20,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select SERIRQ_CONTINUOUS_MODE
 	select MAINBOARD_HAS_NATIVE_VGA_INIT
 	select EARLY_CBMEM_INIT
+	select MARK_GRAPHICS_MEM_WRCOMB
 
 config MAINBOARD_DIR
 	string