drm/amd/display: Power down hardware if timer not trigger

[WHY]
In headless systems, if SetMode/Power down timer
is not called, hardware will not be powered down
causing HW/SW discrepancies. Powering down hardware
on SetPowerState to D3 will ensure SW/HW state is accurate.

[HOW]
If PowerDownThread timer is not trigger but OS call
SetPowerState to D3, power down hardware.

Reviewed-by: Eric Yang <Eric.Yang2@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Paul Hsieh <paul.hsieh@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>