ACPICA: Remove obsolete GPE function

Remove acpi_hw_write_gpe_enable_reg, it had been reduced down to a
single line of code, and called from only one place.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>