drm: bridge: dw-hdmi: Add support for custom PHY configuration

The DWC HDMI TX controller interfaces with a companion PHY. While
Synopsys provides multiple standard PHYs, SoC vendors can also integrate
a custom PHY.

Modularize PHY configuration to support vendor PHYs through platform
data. The existing PHY configuration code was originally written to
support the DWC HDMI 3D TX PHY, and seems to be compatible with the DWC
MLP PHY. The HDMI 2.0 PHY will require a separate configuration
function.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170303172007.26541-8-laurent.pinchart+renesas@ideasonboard.com