x86/mce: allow mce_barrier_{enter,exit} to return without waiting

x86/mce: allow mce_barrier_{enter,exit} to return without waiting

Add a 'wait' argument to mce_barrier_{enter,exit}() to specify whether
the barrier functions should return immediately without waiting
mce_barrier_{enter,exit}() on other CPUs. This is useful when handling
LMCE, where mce_barrier_{enter,exit} are called only on one CPU.

Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>