drm/amd/display: Don't set dram clock change requirement for SubVP

[Description]
In general cases we want to keep the dram clock change requirement (we
prefer configs that support MCLK switch). Only override to false for
SubVP.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>