MFC r267226:
Initialize the pbuf counter for directio using SYSINIT.
Mark ffs_rawread.c as requiring both ffs and directio options to be
compiled into the kernel. Add ffs_rawread.c to the list of ufs.ko
module' sources.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Fix module build after r243245.

Retire opt_ffs_broken_fixme.h.
Instead of directly calling ffs_snapgone(), use UFS_SNAPGONE() with
usual layering.

Requested by: bde
MFC after: 1 week

Remove opt_mac.h generation for various kernel modules that no longer
require it.

Submitted by: pjd

Allow this module to get its options from the kernel build directory
instead of always hard coding them in CFLAGS. POLA is kept here:
The module file built with GENERIC stays the same.

Tested with: md5(1)

Hook up gjournal bits to the build.

Sponsored by: home.pl

Remove ufs_ihash.c here as well.

Add a few missing opt_ files to make this module compile again.

Add a makefile for building UFS as a module. Since it is of marginal
use it is not built by default, and there are currently bugs that
prevent UFS from being unloaded. Nevertheless it can be useful when
developing UFS code on network-booted machines.