drm/amd/display: Align static screen idle worker with IPX mode

[Why]
Idle worker thread serves for periodic detection of HPD while system is in IPS2.
Currently it is used in headless and static screen scenarios.
IPX can be configured not to execute IPS2 for static screen.
In this case idle worker is redundant.

[How]
Only use periodic detection for static screen if IPS is fully enabled.

Reviewed-by: Sun peng Li <sunpeng.li@amd.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>