gril: Added support for RADIO_STATE_CHANGED

Added support for the unsolicited RADIO_STATE_CHANGED
message, which includes an undocumented radio_state (int32)
as its event data.
plugins: Re-factor ril power & SIM detection logic

Re-factor the plugin to only send a GET_SIM_STATUS
request once the radio has been confirmed to be on.
This closes a race condition during power on which
has caused intermittent erros with both SIM status
and SIM IO.