USB: cdc: add serial-state defines

Add defines for the serial-state bitmap values from section 6.3.5
SerialState of the CDC specification version 1.1.

Note that the bTxCarrier and bRxCarrier bits have been named after their
RS-232 signal equivalents DSR and DCD.

Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20220725075841.1187-3-johan@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>