arm64: locks: Remove CONFIG_GENERIC_LOCKBREAK

Commit 52ea2a56 (arm64: locks: introduce ticket-based spinlock
implementation) introduces the arch_spin_is_contended() function making
CONFIG_GENERIC_LOCKBREAK unnecessary.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>