sub-page blocksize support in iomap non-buffer head path v3

[Christoph Hellwig <hch@xxxxxx>]

Hi all,

this series adds support for buffered I/O without buffer heads for
block size < PAGE_SIZE to the iomap and XFS code.

A git tree is available at:

    git://git.infradead.org/users/hch/xfs.git xfs-iomap-read xfs-remove-bufferheads.2

Gitweb:

    http://git.infradead.org/users/hch/xfs.git/shortlog/refs/heads/xfs-remove-bufferheads.2

Changes since v2:
 - rebased

Changes since v1:
 - call iomap_page_create in page_mkwrite to fix generic/095
 - split into a separate series