USB: cdc_acm: Silence "It is not a modem." error for pbLua devices

The pbLua console port is known to not be a modem, so it is
unnecessary to be told this when it is plugged in.

Add NOT_A_MODEM quirk to tell the driver that we know this already
and hence not to warn us, and mark the pbLua console port.

Signed-off-by: Julian Calaby <julian.calaby@gmail.com>
Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>