Add powergate/powerungate callbacks for gm20b configuration. Change-Id: Ieb681b74de7ea19d172922ef68260be81b675a56 Signed-off-by: Seshendra Gadagottu <sgadagottu@nvidia.com> Reviewed-on: http://git-master/r/457352 Reviewed-by: Automatic_Commit_Validation_User GVS: Gerrit_Virtual_Submit Reviewed-by: Bo Yan <byan@nvidia.com>