Increase default PRBS_TIME for FW

Cronus looked fine with 0x100, but FW appeared
to need about 0x400 for consistent results

Change-Id: I9fc0eec9f4936bdd7852610af9af0feb0f6911ce
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/85333
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Reviewed-by: STEPHEN GLANCY <sglancy@us.ibm.com>
Reviewed-by: Devon A Baughen <devon.baughen1@ibm.com>
Tested-by: Hostboot CI <hostboot-ci+hostboot@us.ibm.com>
Reviewed-by: Louis Stermole <stermole@us.ibm.com>
Tested-by: HWSV CI <hwsv-ci+hostboot@us.ibm.com>
Reviewed-by: Jennifer A Stofer <stofer@us.ibm.com>
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/85365
Reviewed-by: Daniel M Crowell <dcrowell@us.ibm.com>

src/import/generic/procedures/xml/attribute_info/generic_memory_attributes.xml

@@ -411,8 +411,9 @@
       The time to send pre-ipl PRBS in ms.
     </description>
     <valueType>uint32</valueType>
-    <default>0x100</default>
+    <default>0x400</default>
     <platInit/>
+    <mrwHide/>
     <mssAccessorName>omi_dl_preipl_prbs_time</mssAccessorName>
   </attribute>