drm: Eliminate the useless "non-RGB fb" debug message

drm: Eliminate the useless "non-RGB fb" debug message

No point in spamming the log whenever a non-RGB fb is being
constructed. And since there's nothing to do anymore that
fb->bits_per_pixel and fb->depth are gone, we can just kill
off this entire piece of code.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1479498793-31021-36-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>