ofono: base: use g_warning rather than g_error

Open-webOS-DCO-1.0-Signed-off-by: Simon Busch <morphis@gravedo.de>
Rework power state handling regarding service initialization

* LS2 service is now registered from the start and not when the driver is ready
* ofono driver reports readiness when the modem is powered

Open-webOS-DCO-1.0-Signed-off-by: Simon Busch <morphis@gravedo.de>
ofono: correctly depend on ofono dbus service availability

Open-webOS-DCO-1.0-Signed-off-by: Simon Busch <morphis@gravedo.de>