fat: add setlease file operation

fat: add setlease file operation

Add the setlease file_operation to fat_file_operations and
fat_dir_operations, pointing to generic_setlease.  A future patch will
change the default behavior to reject lease attempts with -EINVAL when
there is no setlease file operation defined. Add generic_setlease to
retain the ability to set leases on this filesystem.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260108-setlease-6-20-v1-9-ea4dec9b67fa@kernel.org
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>