Added comments : gic.c, gic.h

Modify gic.c's 211 lines 
-        _gic.ba_gicd[GICD_IPRIORITYR | i / 4] = GIC_INT_PRIORITY_DEFAULT_WORD;
+        _gic.ba_gicd[GICD_IPRIORITYR + i / 4] = GIC_INT_PRIORITY_DEFAULT_WORD;

I thinks it is miss typing.