Implemented flush for Serial UART API

platforms/common/Serial.cpp

@@ -80,6 +80,11 @@ ssize_t Serial::write(const void *buffer, size_t buffer_size)
 	return _impl.write(buffer, buffer_size);
 }
 
+void Serial::flush()
+{
+	return _impl.flush();
+}
+
 uint32_t Serial::getBaudrate() const
 {
 	return _impl.getBaudrate();

platforms/common/include/px4_platform_common/Serial.hpp

@@ -64,6 +64,8 @@ public:
 
 	ssize_t write(const void *buffer, size_t buffer_size);
 
+	void flush();
+
 	// If port is already open then the following configuration functions
 	// will reconfigure the port. If the port is not yet open then they will
 	// simply store the configuration in preparation for the port to be opened.