drm/amd/display: Calc DLG from dummy p-state if full p-state unsupported

[Why]
Currently, when full p-state changes are not supported, DLG parameters
are calculated for no p-state support at all. However, we are required
to always support dummy p-state changes, so we should instead calculate
DLG based on dummy p-state latency when full p-state is unsupported.
This behaviour already exists for DCN2.

[How]
 - move DLG calculation inside WM calculation
 - if p-state unsupported, do not recalculate for set A, instead copy from
set C, and perform DLG calculation with dummy p-state latency

Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>