ntfs: update iomap and address space operations

Update the address space operations to use the iomap framework,
replacing legacy buffer-head based code.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>