Make ZVOL writes in device mode support IO_SYNC flag.

MFC after:	1 month


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271308 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Improve cache control support, including DPO/FUA flags and the mode page.

At this moment it works only for files and ZVOLs in device mode since BIOs
have no respective respective cache control flags (DPO/FUA).

MFC after:	1 month
Sponsored by:	iXsystems, Inc.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271309 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f