IB/hfi1: Remove HFI1_VERBS_31BIT_PSN option

Remove HFI1_VERBS_31BIT_PSN Kconfig option leaving only 31-bit PSNs
available. The option was implemented in the early days of the driver
and is no longer needed.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Grzegorz Morys <grzegorz.morys@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>