mraa: initial implementation of "hooks"

* Should allow for more platform quirks to be handled by mraa without
* massive conditional areas per platform.

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>

include/mraa_internal.h

@@ -25,6 +25,8 @@
 #pragma once
 
 #include "common.h"
+#include "mraa_adv_func.h"
+#include "mraa_internal_types.h"
 
 /** Setup gpio
  *
@@ -76,3 +78,9 @@ mraa_mmap_pin_t* mraa_setup_mmap_gpio(int pin);
  * @return out direction to setup. 1 for output 0 for input
  */
 mraa_result_t mraa_swap_complex_gpio(int pin, int out);
+
+/** Get the advance structure.
+ *
+ * @return struct containing internal advance information for hooks
+ */
+mraa_adv_func* mraa_get_advance();