x86: Remove MARK_GRAPHICS_MEM_WRCOMB

MARK_GRAPHICS_MEM_WRCOMB is not referenced anywhere in the code,
hence remove it.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>

arch/x86/Kconfig

@@ -188,14 +188,6 @@ config X86_RAMTEST
 	  to work correctly. It is not exhaustive but can save time by
 	  detecting obvious failures.
 
-config MARK_GRAPHICS_MEM_WRCOMB
-	bool "Mark graphics memory as write-combining"
-	default n
-	help
-	  The graphics performance may increase if the graphics
-	  memory is set as write-combining cache type. This option
-	  enables marking the graphics memory as write-combining.
-
 config HAVE_FSP
 	bool "Add an Firmware Support Package binary"
 	help

board/google/chromebook_link/Kconfig

@@ -22,7 +22,6 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select NORTHBRIDGE_INTEL_IVYBRIDGE
 	select SOUTHBRIDGE_INTEL_C216
 	select HAVE_ACPI_RESUME
-	select MARK_GRAPHICS_MEM_WRCOMB
 	select BOARD_ROMSIZE_KB_8192
 
 config PCIE_ECAM_BASE

board/google/chromebox_panther/Kconfig

@@ -23,7 +23,6 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select NORTHBRIDGE_INTEL_IVYBRIDGE
 	select SOUTHBRIDGE_INTEL_C216
 	select HAVE_ACPI_RESUME
-	select MARK_GRAPHICS_MEM_WRCOMB
 	select BOARD_ROMSIZE_KB_8192
 
 config SYS_CAR_ADDR