Add an option to use LowPowerTimer for poll

Author: amq

platform/mbed_lib.json

@@ -34,6 +34,11 @@
         "force-non-copyable-error": {
             "help": "Force compile time error when a NonCopyable object is copied",
             "value": false
+        },
+
+        "poll-use-lowpower-timer": {
+            "help": "Enable use of low power timer class for poll(). May cause missing events.",
+            "value": false
         }
     },
     "target_overrides": {

platform/mbed_poll.cpp

@@ -34,7 +34,11 @@ int poll(pollfh fhs[], unsigned nfhs, int timeout)
      * interested in. In future, his spinning behaviour will be replaced with
      * condition variables.
      */
+#if MBED_CONF_PLATFORM_POLL_USE_LOWPOWER_TIMER
+    LowPowerTimer timer;
+#else
     Timer timer;
+#endif
     if (timeout > 0) {
         timer.start();
     }