drm: bridge: dw-hdmi: Detect PHY type at runtime

Detect the PHY type and use it to handle the PHY type-specific SVSRET
signal.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170117082910.27023-17-laurent.pinchart+renesas@ideasonboard.com