Add settings for SUW data control.

While the device is being provisioned we can default to
mobile-data-off and let the provisioning app turn mobile
data back on if the user wants it.  After provisioning
control is restored.

Settings in play:
Settings.Global.DEVICE_PROVISIONED (existing)
SystemProperty ro.com.android.mobiledata (existing)
Settings.Global.MOBILE_DATA (existing)

SystemProperty ro.com.android.prov_mobiledata (new)
Settings.Global.DEVICE_PROVISIONING_MOBILE_DATA_ENABLED (new)

If the new settings aren't used, the old behvior is used.

bug:26638209
Change-Id: I4bac52632f757f7132c69c427226ce1cdaccfd44