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.

include/nuttx/irq.h

@@ -55,7 +55,7 @@
  */
 
 #ifndef __ASSEMBLY__
-# define irq_detach(isr) irq_attach(isr, NULL)
+# define irq_detach(isr) irq_attach(isr, NULL, NULL)
 #endif
 
 /****************************************************************************
@@ -65,7 +65,7 @@
 /* This struct defines the way the registers are stored */
 
 #ifndef __ASSEMBLY__
-typedef int (*xcpt_t)(int irq, FAR void *context);
+typedef int (*xcpt_t)(int irq, FAR void *context, FAR void *arg);
 #endif
 
 /* Now include architecture-specific types */
@@ -94,11 +94,11 @@ extern "C"
  *
  * Description:
  *   Configure the IRQ subsystem so that IRQ number 'irq' is dispatched to
- *   'isr'
+ *   'isr' with argument 'arg'
  *
  ****************************************************************************/
 
-int irq_attach(int irq, xcpt_t isr);
+int irq_attach(int irq, xcpt_t isr, FAR void * arg);
 
 /****************************************************************************
  * Name: enter_critical_section