google/slippy: Don't force native graphics init

The board dutifully registers an int15h handler and provides the
defaults to add a VGABIOS.
That should be good enough to initialize graphics through the VGABIOS
file.

Fixes build on Chrome OS configurations (at least until the Ada toolchain
situation is resolved over there).

Change-Id: I1d956b5a163b7cdf2bd467197fba95f16e5e8fa3
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/20218
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>

src/mainboard/google/slippy/Kconfig

@@ -21,7 +21,6 @@ if BOARD_GOOGLE_BASEBOARD_SLIPPY
 config VBOOT
 	select EC_GOOGLE_CHROMEEC_SWITCHES
 	select VBOOT_LID_SWITCH
-	select MAINBOARD_FORCE_NATIVE_VGA_INIT
 	select VBOOT_VBNV_CMOS
 
 config MAINBOARD_DIR