drm/amd/display: update clk for various HDMI color depths

[why]
When programming tonga's connector's backend we didn't take
in account that HDMI's colour depth might be more than 8bpc
therefore we need to add a switch statement that would adjust
the pixel clock accordingly.

[how]
Add a switch statement updating clock by its appropriate
coefficient.

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org