update kernel mkfile.  add rb, depricate alphapc and bitsy

Reference: /n/atom/patch/applied2013/mk920130813
Date: Tue Aug 13 21:47:13 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/mkfile	Tue Aug 13 21:46:50 2013
+++ /sys/src/9/mkfile	Tue Aug 13 21:46:50 2013
@@ -1,14 +1,15 @@
 ARCH=\
 	bcm\
-	alphapc\
-	bitsy\
+#	alphapc\
+#	bitsy\
 	kw\
 	mtx\
 	omap\
 	pc\
 	pcpae\
+	rb\
 #	ppc\
-#	teg2\
+	teg2\
 	
 all:V:
 	for(i in $ARCH)@{