drm/virtio: Call drm_helper_mode_fill_fb_struct() before drm_framebuffer_init()

drm/virtio: Call drm_helper_mode_fill_fb_struct() before drm_framebuffer_init()

We want framebuffers to be mostly useable already before
drm_framebuffer_init() get called, and so we will start demanding that
all the interesting format/size/etc. information be filled in before
drm_framebuffer_init(). drm_helper_mode_fill_fb_struct() will do that
for us, so let's make sure it gets called before drm_framebuffer_init().

Cc: Dave Airlie <airlied@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1479498793-31021-17-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>