[IA64] Squeeze ticket locks back into 4 bytes.

Linus pointed out that other people have spent large amounts of time
and effort to optimize the layout of frequently used structures. Often
these have embedded locks, and the assumption is that a lock takes
4 bytes.  Linus also pointed out how to work with the limited options
for atomic instructions on Itanium.

Signed-off-by: Tony Luck <tony.luck@intel.com>