ACPICA: Events: Always modify GPE registers under the GPE lock

It is reported that there are pieces of code invoking acpi_ev_finish_gpe()
without holding acpi_gbl_gpe_lock. Since this function will modify GPE
register values, there could be races breaking the register modification
process.

This patch fixes this issue. Lv Zheng.

Reported-by: Joe Liu <joe.liu@apple.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>