Calculate sha256 sums for miniroots.

OK patrick@, bmercer@

src/etc/etc.beagle/Makefile.inc

@@ -1,5 +1,6 @@
-#	$OpenBSD: Makefile.inc,v 1.2 2013/05/30 15:57:25 florian Exp $
+#	$OpenBSD: Makefile.inc,v 1.3 2013/06/22 10:12:11 florian Exp $
 
 bootblocks:
 
-MDEXT=	bsd.rd
+MDEXT=	bsd.rd miniroot-am335x-${OSrev}.fs miniroot-beagle-${OSrev}.fs \
+	miniroot-panda-${OSrev}.fs