sun6i: dsi: Convert to generic phy handling

Now that we have everything in place in the PHY framework to deal in a
generic way with MIPI D-PHY phys, let's convert our PHY driver and its
associated DSI driver to that new API.

Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/dc6450e2978b6dafcc464595ad06204d22d2658f.1548085432.git-series.maxime.ripard@bootlin.com