Added Qurt platform Serial implementations for bytesAvailable() and flush(). (#25348)

platforms/qurt/src/px4/SerialImpl.cpp

@@ -39,6 +39,11 @@
 
 #define MODULE_NAME "SerialImpl"
 
+extern "C" {
+	__EXPORT int fc_uart_rx_available(int fd, uint32_t *data);
+	__EXPORT int fc_uart_flush_rx(int fd);
+}
+
 namespace device
 {
 
@@ -160,9 +165,14 @@ bool SerialImpl::close()
 
 ssize_t SerialImpl::bytesAvailable()
 {
-	// TODO:
-	PX4_WARN("bytesAvailable not implemented!");
-	return 0;
+	if (!_open) {
+		PX4_ERR("Device not open!");
+		return -1;
+	}
+
+	uint32_t rx_bytes = 0;
+	(void) fc_uart_rx_available(_serial_fd, &rx_bytes);
+	return (ssize_t) rx_bytes;
 }
 
 ssize_t SerialImpl::read(uint8_t *buffer, size_t buffer_size)
@@ -267,7 +277,9 @@ ssize_t SerialImpl::write(const void *buffer, size_t buffer_size)
 
 void SerialImpl::flush()
 {
-	// TODO: Flush not implemented yet on Qurt
+	if (_open) {
+		(void) fc_uart_flush_rx(_serial_fd);
+	}
 }
 
 const char *SerialImpl::getPort() const