BPM: Bpm::issueCommand() fixes

- Fixes an issue where it was possible to send commands to the BPM via
::issueCommand() without having set the correct magic values first. This
will prevent a rare issue from occurring during a recovery path.

- Adds retry logic to ::issueCommand() where the command will be resent
when the BPM returns an error in the command status register.

Change-Id: I7cc792e298fc81d05717ed72289df57856985e33
CQ:SW483466
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/92531
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
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: Daniel M Crowell <dcrowell@us.ibm.com>