drm/amd/display: Add a check for idle power optimization

[why]
Need a helper function to check idle power is allowed
so that dc doesn't access any registers that are power-gated.

[how]
Implement helper function to check idle power optimization.
Enable a hook to check if detection is allowed.

V2:
Add function hooks for set and get idle states.
Check if function hook was properly initialized.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Reviewed-by: Nicholas Choi <nicholas.choi@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Sung Joon Kim <sungkim@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>