Enable CONFIG_GFXUMA for roda/rk886ex

Without GFXUMA beeing set, MTRR initialization runs out of variable MTRRs.

Change-Id: I5d1aa0d5fa2d72f17a0d88cae3fad880b489828c
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: http://review.coreboot.org/1086
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/mainboard/roda/rk886ex/Kconfig

@@ -22,6 +22,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select HAVE_ACPI_RESUME
 	select BOARD_ROMSIZE_KB_1024
 	select CHANNEL_XOR_RANDOMIZATION
+	select GFXUMA
 
 config MAINBOARD_DIR
 	string