[SCSI] lpfc 8.3.2 : Addition of SLI4 Interface - Mailbox handling

The mailbox commands themselves are the same, or very similar to
their SLI3 counterparts. This patch genericizes mailbox command
handling and adds support for the new SLI4 mailbox queue.

Signed-off-by: James Smart <james.smart@emulex.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>