SamsungQualcomm RILs: throttle multiple outstanding SEND_SMS requests

  * Our radio generates a GenericFailure if a SEND_SMS request is sent
    before the previous SEND_SMS has completed.
  * Add a variable to track whether a SEND_SMS is in progress.
  * In sendSMS(), wait for the previous SEND_SMS to finish. Block for
    up to 30 seconds. If this passes with no response, blindly send the
    next SEND_SMS and let normal error handling take over.
  * In responseSMS(), notify that the SEND_SMS is complete.
  * Same thing above for the CDMA RIL
  * Algorithm credit Mike Kasick

Change-Id: I7beadc809a9e35fa100e5823bdfc3e9879ab3233