drm: bridge: dw-hdmi: Move HPD handling to PHY operations

The HDMI TX controller support HPD and RXSENSE signaling from the PHY
via it's STAT0 PHY interface, but some vendor PHYs can manage these
signals independently from the controller, thus these STAT0 handling
should be moved to PHY specific operations and become optional.

The existing STAT0 HPD and RXSENSE handling code is refactored into
a supplementaty set of default PHY operations that are used automatically
when the platform glue doesn't provide its own operations.

Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1491309119-24220-2-git-send-email-narmstrong@baylibre.com