MLK-16918-5: drm: Implement NWL MIPI-DSI as a real drm_bridge

MLK-16918-5: drm: Implement NWL MIPI-DSI as a real drm_bridge

Currently, the Northwest Logic MIPI-DSI controller host specific code
resides under drm/bridge, but is not a real drm_bridge. It creates a
drm_bridge and adds itself to the drm_encoder that handles this file,
but this is wrong, since it does not implement the drm_bridge_funcs.

The correct way to implement a drm_bridge is to add the drm_bridge and
let other components (another bridge or a drm_encoder) to attach to this
bridge.
Since we are doing this, a new compatible strings can be used for this
driver: "nwl,mipi-dsi".

Since this was used by nwl_dsi-imx.c, update that driver to use this
bridge correctly.

This is needed in order to add support for MIPI-DSI on 8MQ. The IMX_NWL
driver will either add a DSI encoder to DRM, or a DSI bridge.
The encoder will be used by imx-drm-core driver, while the bridge
will be used by MXSFB driver (which creates a simple display pipe).

Signed-off-by: Robert Chiras <robert.chiras@nxp.com>