locking/atomics/openrisc: Don't pull in all of <linux/bitops.h> in <asm/cmpxchg.h>

The openrisc implementation of <asm/cmpxchg.h> pulls in <linux/bitops.h>,
so that it can refer to BITS_PER_BYTE. It also transitively relies on
this pulling in <linux/compiler.h> for READ_ONCE().

Replace the #include with <linux/bits.h> and <linux/compiler.h>.

Signed-off-by: Will Deacon <will.deacon@arm.com>
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/1529412794-17720-5-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>