drm/amd/display: fix system hang when PSR exits

drm/amd/display: fix system hang when PSR exits

[why]
When DC driver send PSR exit dmub command to DMUB FW, it might not
wait until PSR exit. Then it may hit the following deadlock situation.
1. DC driver send HW LOCK command to DMUB FW due to frame update
2. DMUB FW Set the HW lock
3. DMUB execute PSR exit sequence and stuck at polling DPG Pending
register due to the HW Lock is set
4. DC driver ask DMUB FW to unlock HW lock, but DMUB FW is polling
DPG pending register

[how]
The reason why DC driver doesn't wait until PSR exit is because some of
the PSR state machine state is not update the dc driver. So when DC
driver read back the PSR state, it take the state for PSR inactive.

Signed-off-by: David Zhang <dingchen.zhang@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>