mraa.c: add a by-name lookup function also for UARTs

Signed-off-by: Tapani Utriainen <tapani@technexion.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

api/mraa/common.h

@@ -265,6 +265,14 @@ int mraa_spi_lookup(const char* spi_name);
  */
 int mraa_pwm_lookup(const char* pwm_name);
 
+/**
+ * Get UART index by name, board must be initialised.
+ *
+ * @param uart_name: Name of UART. Eg:UART1
+ * @return int of MRAA index for UART, or -1 if not found.
+ */
+int mraa_uart_lookup(const char* uart_name);
+
 /**
  * Get default i2c bus, board must be initialised.
  *