Initial: GSM: support GNSS operations

Author: facchinm

libraries/GSM/src/GSM.cpp

@@ -74,6 +74,10 @@ void arduino::GSMClass::end() {
 
 }
 
+void arduino::GSMClass::startGNSS(mbed::Callback<void(char*)> gnss_cb) {
+  (static_cast<mbed::GEMALTO_CINTERION_CellularStack*>(_context->get_stack()))->startGNSS(gnss_cb);
+}
+
 int arduino::GSMClass::disconnect() {
   return 0;
 }

libraries/GSM/src/GSM.h

@@ -73,6 +73,8 @@ class GSMClass : public MbedSocketClass {
 
   void debug(Stream& stream);
 
+  void startGNSS(mbed::Callback<void(char*)> gnss_cb);
+
   int ping(const char* hostname, uint8_t ttl = 128);
   int ping(const String& hostname, uint8_t ttl = 128);
   int ping(IPAddress host, uint8_t ttl = 128);