drm/bridge: Add NWL MIPI DSI host controller support

This adds initial support for the NWL MIPI DSI Host controller found on
i.MX8 SoCs.

It adds support for the i.MX8MQ but the same IP can be found on
e.g. the i.MX8QXP.

It has been tested on the Librem 5 devkit using mxsfb.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Co-developed-by: Robert Chiras <robert.chiras@nxp.com>
Signed-off-by: Robert Chiras <robert.chiras@nxp.com>
Tested-by: Robert Chiras <robert.chiras@nxp.com>
Tested-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1cf5750f734e33d005564cd89c576eaf3c1c192b.1586427783.git.agx@sigxcpu.org