drm/amd/display: Add basic infrastructure for enabling FAMS

We want to enable Firmware Assisted Memory (FAMS) Switching, but first,
we need to add the required code infrastructure in DC before allowing it
in amdgpu_dm.

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>