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.

Signed-off-by: Sung Joon Kim <Sungjoon.Kim@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>