drm/amd/display: Allow idle optimization after turning off all pipes

[Why]
In certain D3 cases (BOCO / BOMACO) the hardware is reset but
software state still has idle_optimizations = true. This prevents
us from entering idle optimizations again if no display is connected.

[How]
In hw init, reset the idle optimization state, and allow idle
optimizations after all pipes have been turned off.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>