gpio : Add support for input pull up/down modes

Make use of 'active_low' interface in sysfs for configuring input pin
in pull up / pull down mode. C++ binding also has been added.

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

api/mraa/gpio.h

@@ -84,6 +84,14 @@ typedef enum {
     MRAA_GPIO_EDGE_FALLING = 3 /**< Interrupt on falling only */
 } mraa_gpio_edge_t;
 
+/**
+ * Gpio input modes
+ */
+typedef enum {
+    MRAA_GPIO_ACTIVE_HIGH = 0, /**< Resistive High */
+    MRAA_GPIO_ACTIVE_LOW = 1,  /**< Resistive Low */
+} mraa_gpio_input_mode_t;
+
 /**
  * Initialise gpio_context, based on board number
  *
@@ -218,6 +226,16 @@ int mraa_gpio_get_pin(mraa_gpio_context dev);
  */
 int mraa_gpio_get_pin_raw(mraa_gpio_context dev);
 
+/**
+ * Set Gpio input mode
+ *
+ * @param dev The Gpio context
+ * @param mode Mode to set input pin state
+ * @return Result of operation
+ */
+mraa_result_t mraa_gpio_input_mode(mraa_gpio_context dev, mraa_gpio_input_mode_t);
+
+
 #ifdef __cplusplus
 }
 #endif