drm/amd/display: Set OPP default values in init_hw

On S3 resume, we do not reconstruct OPP, but we do need to
reinitialize some of its values to the default ones.
Therefore, move those lines out of the OPP constructor and
into init_hw.

Also reset the hubp power gated flag, since nothing is
power gated at init_hw.

Signed-off-by: Andrew Jiang <Andrew.Jiang@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>