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>

src/intel_galileo_rev_g.c

@@ -30,7 +30,7 @@
 #include "intel_galileo_rev_g.h"
 
 mraa_board_t*
-mraa_intel_galileo_gen2()
+mraa_intel_galileo_gen2(mraa_adv_func* adv)
 {
     mraa_board_t* b = (mraa_board_t*) malloc(sizeof(mraa_board_t));
     if (b == NULL)