Remove writeable from ATTR_FABRIC_GROUP/CHIP_ID

At one point these attributes had to be writeable to satisfy a
fapi2 requirement in the SBE.  That limitation has been removed
so they are being reverted back to their natural state.

Change-Id: I9f7b8f126844760f623da26cc877e1b3806e386a
CQ: SW426882
Reviewed-on: http://ralgit01.raleigh.ibm.com/gerrit1/58173
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Reviewed-by: Martin Gloff <mgloff@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>
Reviewed-by: Christian R. Geddes <crgeddes@us.ibm.com>
Reviewed-by: Daniel M. Crowell <dcrowell@us.ibm.com>

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

@@ -1065,7 +1065,6 @@
         <default>0</default>
       </uint8_t>
     </simpleType>
-    <writeable></writeable>
   </attribute>
 
   <attribute>
@@ -1087,7 +1086,6 @@
         <default>0</default>
       </uint8_t>
     </simpleType>
-    <writeable></writeable>
   </attribute>
 
   <attribute>