drm/amd/powerplay: add function to set default overdrive settings

Add function of vega20_set_default_od8_setttings for vega20 with smu11
arch to setup default overdrive value.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>