mraa: add a function that returns the number of uarts available

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

src/mraa.c

@@ -750,6 +750,15 @@ mraa_get_platform_version(int platform_offset)
     }
 }
 
+int
+mraa_get_uart_count(void)
+{
+    if (plat == NULL) {
+        return -1;
+    }
+    return plat->uart_dev_count;
+}
+
 int
 mraa_get_i2c_bus_count()
 {