The display backend does not support BGRX8888. There is also no trace
of this in the original list of supported formats before the commit
b636d3f9 ("drm/sun4i: frontend: Add support for the BGRX8888 input
format"). Nor do the backend configuration helpers handle this format.

Remove BGRX8888 from list of supported formats by the backend.

Fixes: 3d4265f8 ("drm/sun4i: backend: Add a helper and a list for supported formats")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190125032314.20915-4-wens@csie.org