[kernel] Re-add channel syscalls

Channels were unused, and while they were listed in syscalls.def, they
had no syscalls listed in their interface. This change adds them back,
and updates them to the curren syscall style.

definitions/objects/channel.def

@@ -1,3 +1,14 @@
 object channel : kobject {
     uid 3ea38b96aa0e54c8
+
+    method create [constructor] 
+    method close [destructor]
+
+    method send {
+        param data buffer [inout]
+    }
+
+    method receive {
+        param data buffer [out]
+    }
 }