s390,alpha: switch to 64-bit ino_t

s390 and alpha are the only 64 bit architectures with a 32-bit ino_t.
Since this is quite unusual this causes bugs from time to time.

See e.g. commit ebce3eb2 ("ceph: fix inode number handling on
arches with 32-bit ino_t") for an example.

This (obviously) also prevents s390 and alpha to use 64-bit ino_t for
tmpfs. See commit b85a7a8b ("tmpfs: disallow CONFIG_TMPFS_INODE64
on s390").

Therefore switch both s390 and alpha to 64-bit ino_t. This should only
have an effect on the ustat system call. To prevent ABI breakage
define struct ustat compatible to the old layout and change
sys_ustat() accordingly.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>