drm/amd/display: Support uclk switching for DCN2

[Why]
We were previously forcing the uclk for every state to max and reducing
the switch time to prevent uclk switching from occuring. This workaround
was previously needed in order to avoid hangs + underflow under certain
display configurations.

Now that DC has the proper fix complete we can drop the hacks and
improve power for most display configurations.

[How]
We still need the function pointers hooked up to grab the real uclk
states from pplib. The rest of the prior hack can be reverted.

The key requirements here are really just DC support, updated firmware,
and support for disabling p-state support when needed in pplib/smu.

When these requirements are met uclk switching works without underflow
or hangs.

Fixes: 02316e96 ("drm/amd/display: Force uclk to max for every state")

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>