irq_dispatch: Add argument pointer to irq_dispatch

Provide a user defined callback context for irq's, such that when
registering a callback users can provide a pointer that will get
passed back when the isr is called.

configs/pcduino-a10/src/a1x_buttons.c

@@ -142,7 +142,7 @@ xcpt_t board_button_irq(int id, xcpt_t irqhandler)
       /* Configure the interrupt */
 
       a1x_pioirq(xxx);
-      (void)irq_attach(xxx, irqhandler);
+      (void)irq_attach(xxx, irqhandler, NULL);
       a1x_pioirqenable(xxx);
       leave_critical_section(flags);
     }