s390/spinlock: Implement ticket locks (8 Bit tickets)

s390/spinlock: Implement ticket locks (8 Bit tickets)

This patch adds a ticket lock spinlock implementation to s390.
It is controlled by CONFIG_S390_TICKET_SPINLOCK.

The size of arch_spinlock_t is kept (32 bit). Therefore the lock tickets
can have only 8 bits each. Therefore the lock implementation stops to
be fair when the lock is taken and more than 253 CPUs are waiting for it.
But this can be considered a rare case.

[ Martin Schwidefsky: patch breakdown and code beautification ]

Signed-off-by: Philipp Hachtmann <phacht@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>