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/xtrs/src/xtr_irq.c

@@ -70,7 +70,7 @@ void up_irqinitialize(void)
    * xtrs_timer_initialize()
    */
 
-  irq_attach(Z80_IRQ_SYSTIMER, (xcpt_t)xtrs_timerisr);
+  irq_attach(Z80_IRQ_SYSTIMER, (xcpt_t)xtrs_timerisr, NULL);
 
   /* And finally, enable interrupts (including the timer) */
 

configs/xtrs/src/xtr_timerisr.c

@@ -59,7 +59,7 @@
  *
  ****************************************************************************/
 
-int xtrs_timerisr(int irq, FAR chipreg_t *regs)
+int xtrs_timerisr(int irq, FAR chipreg_t *regs, FAR void *arg)
 {
    /* Process timer interrupt */