SBE DMT Message Uses all 4 mbox regs
SBE DMT Message Uses all 4 mbox regs

- Update constant used in SBE PSU message send to indicate
     all 4 regs are used

Change-Id: I905452abf5e2e6e6f739ab2b54b3ef780a950815
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/88859
Reviewed-by: Nicholas E Bofferding <fb8db48116bc8a69e29dd8cdb037246f232f4af5@us.ibm.com>
Tested-by: Jenkins Server <8e3f934e4c44875bc48d33da3ea13d93ba9a233f@us.ibm.com>
Tested-by: Jenkins OP Build CI <e610bd72261d3c0a48f1e8ae36832ab00774d426@us.ibm.com>
Reviewed-by: Ilya Smirnov <2c7a6ec38cfb553b896499595cca9c656159f2a4@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