libsel4utils: Change IRQ server public structs

The structs are updated to account for the new design that's part of the
refactoring. The IRQ details are no longer exposed and the user is
expected to use a pointer to refer to an IRQ server object.
diff --git a/libsel4utils/include/sel4utils/irq_server.h b/libsel4utils/include/sel4utils/irq_server.h
index 3e6f472..beace62 100644
--- a/libsel4utils/include/sel4utils/irq_server.h
+++ b/libsel4utils/include/sel4utils/irq_server.h
@@ -60,25 +60,9 @@
 #include <platsupport/irq.h>
 #include <sel4platsupport/irq.h>
 
-typedef int irq_t;
+typedef struct irq_server irq_server_t;
 
-struct irq_data;
-
-/**
- * @return non-zero if the IRQ should be ACKed
- */
-typedef void (*irq_handler_fn)(struct irq_data* irq);
-
-struct irq_data {
-/// irq number
-    irq_t irq;
-/// The capability for this irq number
-    seL4_CPtr cap;
-/// Client data: function to call when the IRQ arrives
-    irq_handler_fn cb;
-/// Client specific handle to pass to the callback function
-    void* token;
-};
+typedef int thread_id_t;
 
 /**
  * Allows a client to acknowledge an IRQ
@@ -90,8 +74,6 @@
  *** IRQ server node functions ***
  *********************************/
 
-typedef struct irq_server_node* irq_server_node_t;
-
 /**
  * Create a new IRQ server node.
  * @param[in] notification        An notification object that can be used for binding IRQ notification
@@ -124,8 +106,6 @@
  *** IRQ server functions ***
  ****************************/
 
-typedef struct irq_server* irq_server_t;
-
 /**
  * Initialises an IRQ server.
  * The server will spawn threads to handle incoming IRQs. The function of the