tmpfs: fix XATTR N overriding POSIX_ACL Y

Choosing TMPFS_XATTR default N was switching off TMPFS_POSIX_ACL,
even if it had been Y in oldconfig; and Linus reports that PulseAudio
goes subtly wrong unless it can use ACLs on /dev/shm.

Make TMPFS_POSIX_ACL select TMPFS_XATTR (and depend upon TMPFS),
and move the TMPFS_POSIX_ACL entry before the TMPFS_XATTR entry,
to avoid asking unnecessary questions then ignoring their answers.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>