drm/amd/display: Power down hardware if set mode is not called before timeout

[WHY]
In headless systems, if set mode is not called, hardware will not be
powered down on boot, causing HW/SW discrepancies.  Powering down
hardware on boot will ensure SW state is accurate.

[HOW]
Set a timer callback on boot for 10 seconds. If set mode is not called
within that time, power down hardware. Otherwise, do not power down.

Signed-off-by: Sung Lee <sung.lee@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>