mm/filemap: Change filemap_create_page calling conventions

mm/filemap: Change filemap_create_page calling conventions

By moving the iocb flag checks to the caller, we can pass the
file and the page index instead of the iocb.  It never needed the iter.
By passing the pagevec, we can return an errno (or AOP_TRUNCATED_PAGE)
instead of an ERR_PTR.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>