Use db_lookup_proc() in the DDB 'show procvm' command.

This allows processes to be identified by PID as well as a pointer address.

MFC after:	2 weeks
Sponsored by:	DARPA / AFRL

sys/vm/vm_map.c

@@ -4309,7 +4309,7 @@ DB_SHOW_COMMAND(procvm, procvm)
 	struct proc *p;
 
 	if (have_addr) {
-		p = (struct proc *) addr;
+		p = db_lookup_proc(addr);
 	} else {
 		p = curproc;
 	}