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/intel_galileo_rev_g.h

@@ -24,7 +24,9 @@
 
 #pragma once
 
+#include "mraa_adv_func.h"
+
 #define MRAA_INTEL_GALILEO_GEN_2_PINCOUNT 25
 
 mraa_board_t*
-mraa_intel_galileo_gen2();
+mraa_intel_galileo_gen2(mraa_adv_func* adv);