Fix for Issue #7308 (Deep_sleep_lock Ticker.h Issue)

drivers/Ticker.cpp

@@ -53,4 +53,16 @@ void Ticker::handler()
     }
 }
 
+void Ticker::attach_us(Callback<void()> func, us_timestamp_t t)
+{
+    core_util_critical_section_enter();
+    // lock only for the initial callback setup and this is not low power ticker
+    if (!_function && _lock_deepsleep) {
+        sleep_manager_lock_deep_sleep();
+    }
+    _function = func;
+    setup(t);
+    core_util_critical_section_exit();
+}
+
 } // namespace mbed

drivers/Ticker.h

@@ -117,17 +117,7 @@ class Ticker : public TimerEvent, private NonCopyable<Ticker> {
      *  for threads scheduling.
      *
      */
-    void attach_us(Callback<void()> func, us_timestamp_t t)
-    {
-        core_util_critical_section_enter();
-        // lock only for the initial callback setup and this is not low power ticker
-        if (!_function && _lock_deepsleep) {
-            sleep_manager_lock_deep_sleep();
-        }
-        _function = func;
-        setup(t);
-        core_util_critical_section_exit();
-    }
+    void attach_us(Callback<void()> func, us_timestamp_t t);
 
     /** Attach a member function to be called by the Ticker, specifying the interval in microseconds
      *