- Remove a redundant variable in mpt_pci_attach().
- #if 0 the currently unused paired port linking and unlinking of dual
adapters.
- Simplify MSI/MSI-X allocation and release. For a single one, we don't need
to fiddle with the MSI/MSI-X count and pci_release_msi(9) is smart enough
to just do nothing in case of INTx.
- Canonicalize actions taken on attach failure and detach.
- Remove the remainder of incomplete support for older FreeBSD versions.