drm/vc4: dsi: Add support for DSI0

Commit 4b265fe1 upstream.

DSI0 was partially supported, but didn't register with the main
driver, and the code was inconsistent as to whether it checked
port == 0 or port == 1.

Add compatible string and other support to make it consistent.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20201203132543.861591-6-maxime@cerno.tech