drm/bridge/synopsys: dw-hdmi: Add "unwedge" for ddc bus

See the PhD thesis in the comments in this patch for details, but to
summarize this adds a hacky "unwedge" feature to the dw_hdmi i2c bus to
workaround what appears to be a hardware errata.  This relies on a
pinctrl entry to help change around muxing to perform the unwedge.

NOTE that the specific TV this was tested on was the "Samsung
UN40HU6950FXZA" and the specific port was the "STB" port.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190502225336.206885-2-dianders@chromium.org