drm/amd/display: Return invalid state if GPINT times out

[Why]
GPINT timeout is causing PSR_STATE_0 to be returned when it shouldn't.
We must guarantee that PSR is fully disabled before doing hw programming
on driver-side.

[How]
Return invalid state if GPINT command times out. Let existing retry
logic send the GPINT until successful.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Wyatt Wood <wyatt.wood@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>