USB: serial: qcserial: add Dell DW5570 QDL

commit 24d615a694d649aa2e167c3f97f62bdad07e3f84 upstream.

The Dell DW5570 is a re-branded Sierra Wireless MC8805 which will by
default boot with vid 0x413c and pid 0x81a3. When triggered QDL download
mode, the device switches to pid 0x81a6 and provides the standard TTY
used for firmware upgrade.

Signed-off-by: Aleksander Morgado <aleksander@aleksander.es>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>