MFC: r223985

MFC: r223985

- For SAS but neither FC nor SPI controllers default to using MSI/MSI-X
  (still allowing their use to be disabled via device hints though). This
  matches what the corresponding Linux driver provided by LSI does. Tested
  with SAS1064.
- There's no need to keep track of the RIDs used.
- Don't allocate MSI/MSI-X as RF_SHAREABLE.
- Remove a comment which no longer applies since r209599 (MFC'ed to stable/8
  in r210376).
- Assign NULL rather than 0 to pointers.

git-svn-id: svn://svn.freebsd.org/base/stable/8@224816 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f