iio: Remove iio structures from mraa_platform_t

This means that a valid platform is no longer required for iio operations and
therefore this is now only a req for using USBPLAT

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

include/mraa_internal.h

@@ -35,6 +35,7 @@ extern "C" {
 #include "mraa_adv_func.h"
 
 extern mraa_board_t* plat;
+extern mraa_iio_info_t* plat_iio;
 
 /**
  * Takes in pin information and sets up the multiplexors.

include/mraa_internal_types.h

@@ -284,9 +284,10 @@ typedef struct _board_t {
     mraa_pininfo_t* pins;     /**< Pointer to pin array */
     mraa_adv_func_t* adv_func;    /**< Pointer to advanced function disptach table */
     struct _board_t* sub_platform;     /**< Pointer to sub platform */
-    struct _iio* iio_devices; /**< Pointer to IIO devices */
-    uint8_t iio_device_count; /**< IIO device count */
     /*@}*/
 } mraa_board_t;
 
-
+typedef struct {
+    struct _iio* iio_devices; /**< Pointer to IIO devices */
+    uint8_t iio_device_count; /**< IIO device count */
+} mraa_iio_info_t;