Removes overrideonly in a broadcast mode MRW attribute

Change-Id: I5fde81349fcf147bbb17b4e041cb355362c9bbea
CQ:SW418027
Reviewed-on: http://ralgit01.raleigh.ibm.com/gerrit1/54388
Reviewed-by: ANUWAT SAETOW <asaetow@us.ibm.com>
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: HWSV CI <hwsv-ci+hostboot@us.ibm.com>
Tested-by: Hostboot CI <hostboot-ci+hostboot@us.ibm.com>
Reviewed-by: ANDRE A. MARIN <aamarin@us.ibm.com>
Reviewed-by: Jennifer A. Stofer <stofer@us.ibm.com>
Reviewed-on: http://ralgit01.raleigh.ibm.com/gerrit1/54399
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: Daniel M. Crowell <dcrowell@us.ibm.com>

src/import/chips/p9/procedures/xml/attribute_info/memory_mrw_attributes.xml

@@ -629,7 +629,6 @@
     <valueType>uint8</valueType>
     <platInit/>
     <initToZero/>
-    <overrideOnly/>
     <enum> NO = 0, YES = 1 </enum>
     <mssAccessorName>mrw_force_bcmode_off</mssAccessorName>
   </attribute>