msm: mdss: hdmi: fix deep color enable and audio clock

Enable deep color only for msmcobalt platform. Furthermore,
adjust the pixel clock reported to the audio driver when
deep color is enabled so that it matches the clock configured
when the interface is turned on.

CRs-Fixed: 1034047
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>
Change-Id: I48a767f7673defe60156c305e39f1ce4aa44306b