Document r269065, iSCSI redirection handling

Submitted by:	trasz
Sponsored by:	The FreeBSD Foundation
Document r265523, kern.iscsi.fail_on_disconnection

Submitted by:	trasz
Sponsored by:	The FreeBSD Foundation
Document r265524, iSCSI lock contention optimizations.

Submitted by:	trasz
Sponsored by:	The FreeBSD Foundation
Document r265524, iSCSI performance optimizations.

Submitted by:	trasz
Sponsored by:	The FreeBSD Foundation
Expand r262855 to illustrate how to enable the test suite.

Submitted by:	jmmv
Sponsored by:	The FreeBSD Foundation
Remove a generalized sentence regarding iSCSI updates that
should be covered by the past few commits.

Sponsored by:	The FreeBSD Foundation
Minor rewording to the r260385 entry.

Sponsored by:	The FreeBSD Foundation
Document r270892, autofs(5)

Sponsored by:	The FreeBSD Foundation
Document r270810, hptnr(4) update to 1.0.1.

Sponsored by:	The FreeBSD Foundation
Document r270997, zdb(8) included in /rescue.

Sponsored by:	The FreeBSD Foundation
Document r270890, pathchk(1): Ensure bytes >= 128 are considered
non-portable characters.

Sponsored by:	The FreeBSD Foundation
Minor rewording to the r260387 entry.

Sponsored by:	The FreeBSD Foundation
MFC: r270885, r270948

- Nuke unused sdhci_softc.
- Static'ize sdhci_debug local to sdhci.c.
- Const'ify PCI device description strings.
- Nuke redundant resource ID members from sdhci_pci_softc.
- Nuke unused hw.sdhci_pci.debug tunable.
- Add support for using MSI instead of INTx, controllable via the tunable
  hw.sdhci.enable_msi (defaulting to on) and tested with a RICOH R5CE823 SD
  controller.
- Use NULL instead of 0 for pointers.
Document libc updates from illumos and Apple.

Submitted by:	pfg
Sponsored by:	The FreeBSD Foundation