fuse: add renameat2 support

Support RENAME_EXCHANGE and RENAME_NOREPLACE flags on the userspace ABI.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
(cherry picked from commit 1560c974dcd40a8d3f193283acd7cc6aee13dc13)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

 Conflicts:
	fs/fuse/dir.c
	include/uapi/linux/fuse.h
3 files changed