ACPICA: New: acpi_get_gpe_device interface

This function maps an input GPE index to a GPE block device. Also
Added acpi_current_gpe_count to track the current number of GPEs
that are being managed by the ACPICA core (both FADT-based GPEs
and the GPEs contained in GPE block devices.)

Modify drivers/acpi/system.c to use these 2 new interfaces

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>
diff --git a/include/acpi/acpixf.h b/include/acpi/acpixf.h
index be0aa5e..e09c237 100644
--- a/include/acpi/acpixf.h
+++ b/include/acpi/acpixf.h
@@ -265,6 +265,8 @@
 		    u32 gpe_number,
 		    u32 flags, acpi_event_status * event_status);
 
+acpi_status acpi_get_gpe_device(u32 gpe_index, acpi_handle *gpe_device);
+
 acpi_status
 acpi_install_gpe_block(acpi_handle gpe_device,
 		       struct acpi_generic_address *gpe_block_address,