ACPICA: Add new statistics interface.

This patch ports new counters and statistics interface, already
implemented in ACPICA upstream, to Linux.  That helps to reduce
source code differences between Linux and ACPICA upstream.

[rjw: Changelog]
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/acpi/acpixf.h

@@ -140,6 +140,8 @@ ACPI_HW_DEPENDENT_RETURN_STATUS(acpi_status acpi_disable(void))
 acpi_status acpi_get_system_info(struct acpi_buffer *ret_buffer);
 #endif
 
+acpi_status acpi_get_statistics(struct acpi_statistics *stats);
+
 const char *acpi_format_exception(acpi_status exception);
 
 acpi_status acpi_purge_cached_objects(void);