drm/amd/pp: Setup SoftRegsStart before request smu load fw

need to know SoftRegsStart value to visit the register
UcodeLoadStatus to check fw loading state.

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>