ARM: spinlock: use ticket algorithm for ARMv6+ locking implementation

Ticket spinlocks ensure locking fairness by reducing the thundering herd
effect when acquiring a lock. This is especially important on systems
where memory-access times are not necessarily uniform when accessing
the lock structure (for example, on a multi-cluster platform where the
lock is allocated into L1 when a CPU releases it).

This patch implements the ticket spinlock algorithm for ARM, replacing
the simpler implementation for ARMv6+ processors.

Signed-off-by: Will Deacon <will.deacon@arm.com>