drm/amdgpu/swsmu: use new register offsets for smu_cmn.c

Use the per asic offsets so the we don't have to have
asic specific logic in the common code.

Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>