CHROMIUM: drm: bridge/dw_hdmi: switch ddc mode to standard mode

CHROMIUM: drm: bridge/dw_hdmi: switch ddc mode to standard mode

DDC have two modes: fast mode, standard mode. The previous ddc support
patch(https://chromium-review.googlesource.com/#/c/292012/) configure
the ddc to fast mode.

It works rightly in most HDTV case, but I found that ddc would always
failed if I used the VGA->HDMI adapter. And after I switch ddc to
standard mode, no failed anymore. I believe the standard mode could
provide better compatibility.

BUG=chrome-os-partner:34741
TEST=My VGA->HDMI adapter can read edid now

Change-Id: Ia33ade0a4fda998483baf454b9ccb9f31802f6bc
Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/298270
Commit-Ready: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>