drm/amd/display: Removed power down on boot from DCN31

[Why]
Error message on Linux when booting.

[How]
Removed power down on boot from DCN31 HW init
to match DCN10 HW init.

Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Agustin Gutierrez Sanchez <agustin.gutierrez@amd.com>
Signed-off-by: Derek Lai <derek.lai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>