ACPI / ACPICA: Use helper function for computing GPE masks

In quite a few places ACPICA needs to compute a GPE enable mask with
only one bit, corresponding to a given GPE, set.  Currently, that
computation is always open coded which leads to unnecessary code
duplication.  Fix this by introducing a helper function for computing
one-bit GPE enable masks and using it where appropriate.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>