drm/amd/display: Force enable pstate on driver unload

drm/amd/display: Force enable pstate on driver unload

[Why]
During driver unload, it is expected that p-state switching is supported.
If it's not supported, PMFW will hang due to a forced p-state switch. Even
if the current timing does not support p-state normally, we still want to
force allow because the worst that can happen is underflow. This will
match Navi10 behaviour.

[How]
 - new hubbub func to control the force pstate register
 - force allow when releasing display ownership
   - registers are inaccessible after due to m_cgs.hwNotAvailable
 - explicitly disable force signal during hw_init
   - if driver is disabled and re-enabled, register not cleared otherwise

Also, remove DCN3 part of dcn10_init_hw, we will not be going back to it.

Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>