x86: this_cpu_cmpxchg and this_cpu_xchg operations

x86: this_cpu_cmpxchg and this_cpu_xchg operations

Provide support as far as the hardware capabilities of the x86 cpus
allow.

Define CONFIG_CMPXCHG_LOCAL in Kconfig.cpu to allow core code to test for
fast cpuops implementations.

V1->V2:
	- Take out the definition for this_cpu_cmpxchg_8 and move it into
	  a separate patch.

tj: - Reordered ops to better follow this_cpu_* organization.
    - Renamed macro temp variables similar to their existing
      neighbours.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>