drm/bridge: cdns: Convert to phy framework

Now that we have everything we need in the phy framework to allow to tune
the phy parameters, let's convert the Cadence DSI bridge to that API
instead of creating a ad-hoc driver for its phy.
Acked-by: Sean Paul <sean@poorly.run>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/8772ad061f07cd91fa48bb05880095b25eccec08.1548085432.git-series.maxime.ripard@bootlin.com

drivers/gpu/drm/bridge/Kconfig

@@ -30,6 +30,7 @@ config DRM_CDNS_DSI
 	select DRM_KMS_HELPER
 	select DRM_MIPI_DSI
 	select DRM_PANEL_BRIDGE
+	select GENERIC_PHY_MIPI_DPHY
 	depends on OF
 	help
 	  Support Cadence DPI to DSI bridge. This is an internal