drm/bridge: lvds-codec: Implement atomic_get_input_bus_fmts for LVDS encoder

atomic_get_input_bus_fmts is only implemented for LVDS decoders, resulting
that LVDS encoders only support bus format MEDIA_BUS_FMT_FIXED. This
results in warnings like:
mxsfb 21c8000.lcdif: Bridge does not provide bus format, assuming
 MEDIA_BUS_FMT_RGB888_1X24.
Please fix bridge driver by handling atomic_get_input_bus_fmts.

Fix this by reusing lvds_codec_atomic_get_input_bus_fmts currently used
for LVDS decoders. Use RGB888_1X24 for LVDS encoders. This also allows
removing the dedicated struct drm_bridge_funcs for decoders.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230810063229.597533-1-alexander.stein@ew.tq-group.com