drm/amd/display: determine fast update only before commit minimal transition state

[why]
commit minimal transition state would update current
state to new state with surface and stream update
applied. If we determine fast update only after we
have committed the minimal transition state based on
new state, we will skip committing the full new state.

[how]
determine fast update only earlier based on the
actaul currents state. Only skip full commit when
the transition between actual current state and new
state is fast update only.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>