ACPICA: Add comment explaining _SUB removal

ACPICA commit 81a89968f83bfc3b1d0f0f80f2da08ea69646053

Adds a lengthy comment to acpi_get_object_info explaining the removal
of _SUB and why no complex methods can be added ever to this
interface.

Link: https://github.com/acpica/acpica/commit/81a89968Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpica/nsxfname.c

@@ -267,6 +267,13 @@ static char *acpi_ns_copy_device_id(struct acpi_pnp_device_id *dest,
  *
  * Note: Allocates the return buffer, must be freed by the caller.
  *
+ * Note: This interface is intended to be used during the initial device
+ * discovery namespace traversal. Therefore, no complex methods can be
+ * executed, especially those that access operation regions. Therefore, do
+ * not add any additional methods that could cause problems in this area.
+ * this was the fate of the _SUB method which was found to cause such
+ * problems and was removed (11/2015).
+ *
  ******************************************************************************/
 
 acpi_status