ACPICA: exmutex: General cleanup, restructured some code

ACPICA commit c2a7d000b6be34313b1c50c8a718df16113f0f32

Should be no functional change.

Link: https://github.com/acpica/acpica/commit/c2a7d000


Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>