drm/msm: add RGB 30-bit deep color support for HDMI

Check if the TV supports deep color and adjust the
pixel clock accordingly before setting the mode. Also
make sure that this pixel clock is within the limits
of the sink.

Change-Id: I3c44c06ea54b6c49e19c8c41d693000f7c3feeb7
Signed-off-by: Yuan Zhao <yzhao@codeaurora.org>