drm/amd/display: DCN401 full power down in HW init if any link enabled

drm/amd/display: DCN401 full power down in HW init if any link enabled

[Why]
During HW init, certain operations the driver performs are invalid on
enabled hardware in an unknown state (for example, setting all clock
values to minimum when the GPU is actively driving a display). There is
already code present to call HWSS->power_down during init when any link
is enabled in HW, but that function pointer is unpopulated for most asics.
We want to enable this codepath for DCN401, as it resolves the issue with
being unable to drive certain display configs on adapter re-enable, and we
can restore boot optimizations.

[How]
 - add power_down HWSS function for DCN401
 - remove debug bit to disable boot optimizations for DCN401

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>