Set size of callback irq array to IrqCnt

Rather than hard coding the size of the callback array for irqs,
instead set the size to IrqCnt which is defined by the irq enumeration.

hal/api/CAN.h

@@ -203,7 +203,9 @@ public:
         EpIrq,
         AlIrq,
         BeIrq,
-        IdIrq
+        IdIrq,
+
+        IrqCnt
     };
 
     /** Attach a function to call whenever a CAN frame received interrupt is
@@ -246,7 +248,7 @@ protected:
     virtual void lock();
     virtual void unlock();
     can_t               _can;
-    Callback<void()>    _irq[9];
+    Callback<void()>    _irq[IrqCnt];
     PlatformMutex       _mutex;
 };
 

hal/api/SerialBase.h

@@ -55,7 +55,9 @@ public:
 
     enum IrqType {
         RxIrq = 0,
-        TxIrq
+        TxIrq,
+
+        IrqCnt
     };
 
     enum Flow {
@@ -231,7 +233,7 @@ protected:
 #endif
 
     serial_t         _serial;
-    Callback<void()> _irq[2];
+    Callback<void()> _irq[IrqCnt];
     int              _baud;
 
 };