Add support for the 8568 MDS board

This included some changes to common files:
* Add 8568 processor SVR to various places
* Add support for setting the qe bus-frequency value in the dts
* Add the 8568MDS target to the Makefile

Signed-off-by: Andy Fleming <afleming@freescale.com>
diff --git a/Makefile b/Makefile
index d447a96..a9d56ec 100644
--- a/Makefile
+++ b/Makefile
@@ -1739,6 +1739,9 @@
 MPC8555CDS_config:	unconfig
 	@$(MKCONFIG) $(@:_config=) ppc mpc85xx mpc8555cds cds
 
+MPC8568MDS_config:	unconfig
+	@$(MKCONFIG) $(@:_config=) ppc mpc85xx mpc8568mds
+
 PM854_config:	unconfig
 	@$(MKCONFIG) $(@:_config=) ppc mpc85xx pm854