ACPICA: Events: Update GPE handling and initialization code.

1) Eliminate most use of GAS structs, since they are not needed
for GPEs.
2) Allow raw GPE numbers > 255.

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>