Implement line-status handling for Siemens phones as a quirk rather than
spreading such information all over the driver by matching on vendor and
and product ids.

Note that the SIEMENS_PRODUCT_ID_EF81, which was added after the
line-status handling for the other Siemens phones was fixed, might also
need this quirk.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>