locking/atomics/m68k: Don't use <asm-generic/bitops/lock.h>

<asm-generic/bitops/lock.h> is shortly going to be built on top of the
atomic_long_*() API, which introduces a nasty circular dependency for
m68k where <linux/atomic.h> pulls in <linux/bitops.h> via:

	linux/atomic.h
	asm/atomic.h
	linux/irqflags.h
	asm/irqflags.h
	linux/preempt.h
	asm/preempt.h
	asm-generic/preempt.h
	linux/thread_info.h
	asm/thread_info.h
	asm/page.h
	asm-generic/getorder.h
	linux/log2.h
	linux/bitops.h

Since m68k isn't SMP and doesn't support ACQUIRE/RELEASE barriers, we
can just define the lock bitops in terms of the atomic bitops in the
<asm/bitops.h> header.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: yamada.masahiro@socionext.com
Link: https://lore.kernel.org/lkml/1529412794-17720-3-git-send-email-will.deacon@arm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>