drm/amd/display: For SubVP pipe split case use min transition into MPO

[Description]
- For SubVP pipe split case we need to use a minimial transition
  when opening MPO video since we are transitioning from 4 pipes
  to 3 pipes where an OPP for a previous MPCC will change
- Also save and restore mall config when doing fast_validate in case
  there was a shallow copy of the dc->current_state

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>