correct iv_maxGardRecords sizing
correct iv_maxGardRecords sizing

Before this change iv_maxGardRecords was calculated without taking
into account the space used for the GardRecordsBinary header info
(16 bytes) in the GUARD_DATA section in PNOR. This change excludes
the space needed for the header info to calculate the correct amount
of Gard records HB can track in iv_maxGardRecords

Change-Id: I9b6f005d0f7db2acaf40a5600acf0fbfb553407c
CQ:SW547878
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/129921
Reviewed-by: Matt Derksen <7e9f2fc2ed13c4ee3c2ab17f188630a0f557de86@us.ibm.com>
Tested-by: Jenkins OP Build CI <e610bd72261d3c0a48f1e8ae36832ab00774d426@us.ibm.com>
Reviewed-by: Zachary Clark <9de8c4480303b5335cd2a33eefe814615ba3612a@ibm.com>
Tested-by: Jenkins Combined Simics CI <8312af3886dfc9bb930f549023677220805b137e@us.ibm.com>
Tested-by: Jenkins OP HW <0eb0fff262f74a65a832afbcc7b153e391c9a3fd@us.ibm.com>
Tested-by: Jenkins Server <8e3f934e4c44875bc48d33da3ea13d93ba9a233f@us.ibm.com>
Tested-by: FSP CI Jenkins <aa9e4d9ac7cd25905e9c0dd36d4150516e73dd86@us.ibm.com>
Tested-by: Hostboot CI <52521565bd8ea18a2b112942dce4f4220a97c2c8@us.ibm.com>
Reviewed-by: Daniel M Crowell <912029ca9254ac7b5854e56910561d682e1fa2d0@us.ibm.com>

open-power/hostboot,open-power/hostboot,open-power/hostboot,open-power/hostboot,open-power/hostboot