removing the remaining blockdev_direct_IO users

Hi all,

we have 7 users of blockdev_direct_IO and one of the lower-level
__blockdev_direct_IO left, and I'd really like to get rid of them.

The filesystems are affs, fat, hfs, hfsplus, jfs, nilfs2, udf and ocfs2,
and you are the relevant maintainers.  In 7.2 exfat converted entirely
to iomap, which would be a really good example for a "simple" file
system.  Another options especially for the file systems supporting
foreign formats would be to just drop direct I/O support and reduce
the support burden.