Force NO_SWAP for Explorer MMIO word swap for now

Add an explicit default to match the current Simics behavior. I
believe this will change soon to match hardware though.  Also
removed it from the MRW export list since we want to just control
it explicitly.

Change-Id: I593c3c66b59b4d8fc21709d55cbd47266745f21a
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/81584
Tested-by: Jenkins Server <pfd-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>
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Reviewed-by: Daniel M Crowell <dcrowell@us.ibm.com>

src/usr/targeting/common/xmltohb/hb_customized_attrs.xml

@@ -292,6 +292,12 @@
           <default>0</default>
      </attribute>
 
+    <attribute>
+          <id>ATTR_MSS_OCMB_EXP_STRUCT_MMIO_WORD_SWAP</id>
+          <default>NO_SWAP</default><!-- @fixme : RTC: 202491 -->
+          <no_export/>
+    </attribute>
+
     <attribute>
           <id>ATTR_SYSTEM_IPL_PHASE</id>
           <default>HB_IPL</default>