usb: qcserial: refactor device layout selection

Preparing for more supported standard device layouts. Keeping
the matching macros unchanged to avoid breaking stable
backporting of new device additions.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>