Add option to increase VREF step in p9c characterization shmoo

Change-Id: If252482e4d98e784a65ae3f92dd256d21d55f2a2
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/64581
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: STEPHEN GLANCY <sglancy@us.ibm.com>
Reviewed-by: FEIHONG YAN <fyan@us.ibm.com>
Reviewed-by: Jennifer A. Stofer <stofer@us.ibm.com>
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/64592
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: Christian R. Geddes <crgeddes@us.ibm.com>

src/import/chips/centaur/procedures/xml/attribute_info/memory_attributes.xml

@@ -1704,6 +1704,16 @@ firmware notes: none</description>
     <odmChangeable/>
 </attribute>
 
+<attribute>
+    <id>ATTR_CEN_EFF_SCHMOO_VREF_STEP</id>
+    <targetType>TARGET_TYPE_MBA</targetType>
+    <description>Specifies the step size in register ticks for WR_VREF and RD_VREF shmoos.</description>
+    <valueType>uint8</valueType>
+    <writeable/>
+    <odmVisable/>
+    <odmChangeable/>
+</attribute>
+
 <attribute>
     <id>ATTR_CEN_EFF_SCHMOO_WR_EYE_MIN_MARGIN</id>
     <targetType>TARGET_TYPE_MBA</targetType>