drm/amd/display: Add missing WA and MCLK validation

When the commit fff7eb56 ("drm/amd/display: Don't set dram clock
change requirement for SubVP") was merged, we missed some parts
associated with the MCLK switch. This commit adds all the missing parts.

Fixes: fff7eb56

 ("drm/amd/display: Don't set dram clock change requirement for SubVP")
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>