drm/amd/display: do not send commands to DMUB if DMUB is inactive from S3

[Why]
On resume from S3, may get apply_idle_optimizations call while DMUB
is inactive which will just time out.

[How]
Set and track power state in dmub_srv and check power state before
sending commands to DMUB.  Add interface in both dmub_srv and
dc_dmub_srv

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Samson Tam <samson.tam@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>