drm/amd/display: Add FAMS capability to DCN31

DCN31 supports FAMS, but this was not correctly set to the hardware
setup sequence. This commit fixes this issue by setting the MCLK switch
capability based on the feature capability retrieved from the DMUB.

Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>