iomap: Add iomap_invalidate_folio

Keep iomap_invalidatepage around as a wrapper for use in address_space
operations.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>