Drivers must set the quirk_addfb_prefer_host_byte_order quirk to make
the drm_mode_addfb() compat code work correctly on bigendian machines.

If they don't they interpret pixel_format values incorrectly for bug
compatibility, which in turn implies the ADDFB2 ioctl does not work
correctly then.  So block it to make userspace fallback to ADDFB.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20180907073213.20410-1-kraxel@redhat.com