drm/amd/pp: move common function to smu7_smumgr.c

fiji and polaris can share same setup_pwr_virus
function.

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