drm/virtio: make fbdev support really optional

Currently enabling VirtIO DRM support automatically pulls in
fbdev dependency. However this dep is unnecessary since
DRM core already handles this for us (DRM_FBDEV_EMULATION).
Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1468586897-32298-19-git-send-email-tjakobi@math.uni-bielefeld.de

drivers/gpu/drm/virtio/Kconfig

 config DRM_VIRTIO_GPU
 	tristate "Virtio GPU driver"
 	depends on DRM && VIRTIO
-	select FB_SYS_FILLRECT
-	select FB_SYS_COPYAREA
-	select FB_SYS_IMAGEBLIT
         select DRM_KMS_HELPER
-        select DRM_KMS_FB_HELPER
         select DRM_TTM
 	help
 	   This is the virtual GPU driver for virtio.  It can be used with