drm/amd/display: Add support for 1080p SubVP to reduce idle power

- Override the det to adjust microschedule timings allow for
  1080p configs with SubVP
- To lower unnecessary risk, we prevent multi 1080p configs
  from using SubVP, as multi 1080p already has low idle power.
- Count the number of streams to verify that we are in a
  SubVP config before overriding

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Ethan Bitnun <ethan.bitnun@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>