drm/bridge: Add tc358768 driver

Add basic support for the Toshiba TC358768 RGB to DSI bridge.
Not all the features of the TC358768 is implemented by the initial driver:
MIPI_DSI_MODE_VIDEO and MIPI_DSI_FMT_RGB888 is only supported and tested.

Only write is implemented for mipi_dsi_host_ops.transfer.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200131111553.472-3-peter.ujfalusi@ti.com