usb: clarify ACPI spec version and section number for _UPC & _PLD

ACPI spec inserts sections for new features frequently and section
numbers are changed. It is easy to refer to ACPI spec if ACPI version
is available in comments.

There are no functional changes.

Signed-off-by: Alex Hung <alex.hung@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>