Kconfig: Remove obsolete Kconfig symbols from google/intel boards

- CACHE_ROM is no longer used in the coreboot code.  It was removed in
commit 4337020b (Remove CACHE_ROM.)
- CAR_MIGRATION is also no longer used in coreboot code - it was removed
in commit cbf5bdfe (CBMEM: Always select CAR_MIGRATION)
-  MARK_GRAPHICS_MEM_WRCOMB was removed in
commit 30fe6120 (MTRR: Mark all prefetchable resources as WRCOMB)

Change-Id: I8b33a08c256f6b022e57e9af60d0629d9a3ffac8
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: http://review.coreboot.org/12327
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/mainboard/intel/kunimitsu/Kconfig

@@ -4,7 +4,6 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	def_bool y
 	select BOARD_ID_AUTO
 	select BOARD_ROMSIZE_KB_16384
-	select CACHE_ROM
 	select EC_GOOGLE_CHROMEEC
 	select EC_GOOGLE_CHROMEEC_ACPI_MEMMAP
 	select EC_GOOGLE_CHROMEEC_LPC
@@ -16,7 +15,6 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select HAVE_OPTION_TABLE
 	select HAVE_SMI_HANDLER
 	select MAINBOARD_HAS_CHROMEOS
-	select MARK_GRAPHICS_MEM_WRCOMB
 	select MMCONF_SUPPORT
 	select MONOTONIC_TIMER_MSR
 	select SOC_INTEL_SKYLAKE