drm: fix compilations issues introduced by "drm: allow to use mmuless SoC"

Removing MMU configuration flag from DRM make few automatic
build failed when they answer yes to all flags.

Add asm/vga.h file on Blackfin architecture to not broke compilation.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Fixes: 62a0d98a18 ("drm: allow to use mmuless SoC")
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1483789151-6603-1-git-send-email-benjamin.gaignard@linaro.org

drivers/gpu/drm/nouveau/Kconfig

@@ -1,6 +1,6 @@
 config DRM_NOUVEAU
 	tristate "Nouveau (NVIDIA) cards"
-	depends on DRM && PCI
+	depends on DRM && PCI && MMU
         select FW_LOADER
 	select DRM_KMS_HELPER
 	select DRM_TTM