ACPICA: Introduce special struct type for GPE register addresses

Notice that the bit_width, bit_offset and access_width fields in
struct acpi_generic_address are not used during GPE register
accesses any more, so introduce a simplified address structure
type, struct acpi_gpe_address, to represent addresses of GPE
registers and use it instead of struct acpi_generic_address in
struct acpi_gpe_register_info.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>