Allow single dimm configurations in Axone

This attribute was likely copied from Cumulus where single dimm
configurations we invalid. In Axone single dimm configurations should
be valid. I hit this during bringup when I had the simics scripts configured
in a way that was only making a single dimm detectable

Change-Id: I13908a18ba22a63fae74c68f2d43221dce0a07f1
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/73194
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
Reviewed-by: Chen Du <duchen@us.ibm.com>
Reviewed-by: Matt Derksen <mderkse1@us.ibm.com>
Reviewed-by: Corey V. Swenson <cswenson@us.ibm.com>
Reviewed-by: Daniel M. Crowell <dcrowell@us.ibm.com>

src/usr/targeting/common/xmltohb/simics_AXONE.system.xml

@@ -259,7 +259,7 @@
     </attribute>
     <attribute>
         <id>MSS_INTERLEAVE_ENABLE</id>
-        <default>0x06</default>
+        <default>0x07</default>
     </attribute>
     <attribute>
         <id>MSS_MBA_ADDR_INTERLEAVE_BIT</id>