usb: cdc-acm: Add DISABLE_ECHO for Renesas USB Download mode

Renesas R-Car and RZ/G SoCs have a firmware download mode over USB.
However, on reset a banner string is transmitted out which is not expected
to be echoed back and will corrupt the protocol.

Cc: stable <stable@vger.kernel.org>
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Link: https://lore.kernel.org/r/20201111131209.3977903-1-chris.brandt@renesas.com


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