ACPICA: Use spinlock for acpi_{en|dis}able_gpe

Disabling gpe might interfere with gpe detection/handling,
thus producing "interrupt not handled" errors.
Ironically, disabling of GPE from interrupt context is already
under spinlock, so only userspace needs to start using it.

Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>