ACPICA: Events: Dispatch GPEs after enabling for the first time

After being enabled for the first time, the GPEs may have STS bits already
set. Setting EN bits is not sufficient to trigger the GPEs again, so this
patch polls GPEs after enabling them for the first time.
This is a cleaner version on top of the "GPE clear" fix generated according
to Mika's report and Rafael's original Linux based fix. Based on Linux
commit originated from Rafael J. Wysocki, fixed by Lv Zheng.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>