exfat: add nls operations

This adds the implementation of nls operations for exfat.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Git-commit: 370e812b3ec190fa492c9fd5a80c38b086d105c0
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Change-Id: I45054843a9cea05d30f0289f5da3d8d3ecd74e21
Signed-off-by: lixiang <lixiang@codeaurora.org>