Modified gen_accessors script for greater support

Added support for PROC TARGET, only creates accessors for
attributes that have the mssAccessorName xml tag, added support
for other non-mss attrs that don't have [port][dimm] indexes
and that have target types other than MCS, MCBIST, and SYSTEM

Change-Id: I521f381cd06ed99a6147d6c81ab31443351a248a
Original-Change-Id: I6c76f8e7bbc0be1dade3f77f78d3371d16b609b2
Reviewed-on: http://ralgit01.raleigh.ibm.com/gerrit1/44255
Reviewed-by: Louis Stermole <stermole@us.ibm.com>
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: PPE CI <ppe-ci+hostboot@us.ibm.com>
Tested-by: Hostboot CI <hostboot-ci+hostboot@us.ibm.com>
Reviewed-by: JACOB L. HARVEY <jlharvey@us.ibm.com>
Reviewed-by: Matt K. Light <mklight@us.ibm.com>
Reviewed-by: Daniel M. Crowell <dcrowell@us.ibm.com>
Reviewed-by: Jennifer A. Stofer <stofer@us.ibm.com>

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

@@ -3907,6 +3907,24 @@
       </chip>
     </chipEcFeature>
   </attribute>
+
+  <attribute>
+    <id>ATTR_CHIP_EC_FEATURE_MSS_PERIODICS</id>
+    <targetType>TARGET_TYPE_PROC_CHIP</targetType>
+    <description>
+      For Nimbus DD1.** turn off periodics by default (zqcal and memcal).
+      For Nimbus DD2.** it will be attribute driven without any restrictions.
+    </description>
+    <chipEcFeature>
+      <chip>
+        <name>ENUM_ATTR_NAME_NIMBUS</name>
+        <ec>
+          <value>0x20</value>
+          <test>LESS_THAN</test>
+        </ec>
+      </chip>
+    </chipEcFeature>
+  </attribute>
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