ARC: switch to generic bitops

 - !LLSC now only needs a single spinlock for atomics and bitops

 - Some codegen changes (slight bloat) with generic bitops

   1. code increase due to LD-check-atomic paradigm vs. unconditonal
      atomic (but dirty'ing the cache line even if set already).
      So despite increase, generic is right thing to do.

   2. code decrease (but use of costlier instructions such as DIV vs.
      shifts based math) due to signed arithmetic.
      This needs to be revisited seperately.

     arc:
     static inline int test_bit(unsigned int nr, const volatile unsigned long *addr)
                                ^^^^^^^^^^^^
     generic:
     static inline int test_bit(int nr, const volatile unsigned long *addr)
                                ^^^

Link: https://lore.kernel.org/r/20180830135749.GA13005@arm.com


Signed-off-by: Will Deacon <will@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[vgupta: wrote patch based on Will's poc, analysed codegen diffs]
Signed-off-by: Vineet Gupta <vgupta@kernel.org>