Introduce arch_try_cmpxchg64 for 64-bit and 32-bit targets to improve
code using cmpxchg64.  On 64-bit targets, the generated assembly improves
from:

  ab:	89 c8                	mov    %ecx,%eax
  ad:	48 89 4c 24 60       	mov    %rcx,0x60(%rsp)
  b2:	83 e0 fd             	and    $0xfffffffd,%eax
  b5:	89 54 24 64          	mov    %edx,0x64(%rsp)
  b9:	88 44 24 60          	mov    %al,0x60(%rsp)
  bd:	48 89 c8             	mov    %rcx,%rax
  c0:	c6 44 24 62 f2       	movb   $0xf2,0x62(%rsp)
  c5:	48 8b 74 24 60       	mov    0x60(%rsp),%rsi
  ca:	f0 49 0f b1 34 24    	lock cmpxchg %rsi,(%r12)
  d0:	48 39 c1             	cmp    %rax,%rcx
  d3:	75 cf                	jne    a4 <t+0xa4>

to:

  b3:	89 c2                	mov    %eax,%edx
  b5:	48 89 44 24 60       	mov    %rax,0x60(%rsp)
  ba:	83 e2 fd             	and    $0xfffffffd,%edx
  bd:	89 4c 24 64          	mov    %ecx,0x64(%rsp)
  c1:	88 54 24 60          	mov    %dl,0x60(%rsp)
  c5:	c6 44 24 62 f2       	movb   $0xf2,0x62(%rsp)
  ca:	48 8b 54 24 60       	mov    0x60(%rsp),%rdx
  cf:	f0 48 0f b1 13       	lock cmpxchg %rdx,(%rbx)
  d4:	75 d5                	jne    ab <t+0xab>

where a move and a compare after cmpxchg is saved.  The improvements
for 32-bit targets are even more noticeable, because dual-word compare
after cmpxchg8b gets eliminated.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220515184205.103089-3-ubizjak@gmail.com