Introduce ->get_input_bus_fmts() callback to struct dw_mipi_dsi_plat_data
so that vendor drivers can implement specific methods to get input bus
formats for Synopsys DW MIPI DSI.

While at it, implement a generic callback for ->atomic_get_input_bus_fmts(),
where we try to get the input bus formats through pdata->get_input_bus_fmts()
first.  If it's unavailable, fall back to the only format - MEDIA_BUS_FMT_FIXED,
which matches the default behavior if ->atomic_get_input_bus_fmts() is not
implemented as ->atomic_get_input_bus_fmts()'s kerneldoc indicates.
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230821034008.3876938-3-victor.liu@nxp.com