drm/amd/display: Don't adjust VRR unnecessarily

[why]
Do not need to spend time reprogramming DRR if there were no updates to
the parameters.

[how]
Compare the current stream state to the requested one to determine if an
update is required.

In amdgpu_dm the timing_changed flag is set but never used so can remove it.
Similarly, the stream update for VRR is done after dc_commit and should
not update its adjust field until after the update is completed.  The
adjust field is managed by dc_stream_adjust_vmin_vmax and should not be
manually updated in amdgpu_dm.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>