led: Add on board LED support

This patch adds support for using on board LED through sysfs.
Commonly available LED parameters are supported.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

include/mraa_internal_types.h

@@ -241,6 +241,20 @@ struct _iio {
 };
 #endif
 
+/**
+ * A structure representing an LED device
+ */
+struct _led {
+    /*@{*/
+    int count; /**< total LED count in a platform */
+    char *led_name; /**< LED name */
+    char led_path[64]; /**< sysfs path of the LED */
+    int trig_fd; /**< trigger file descriptor */
+    int bright_fd; /**< brightness file descriptor */
+    int max_bright_fd; /**< maximum brightness file descriptor */
+    /*@}*/
+};
+
 /**
  * A bitfield representing the capabilities of a pin.
  */