usb: gadget: Send BRK signal to host on flow disable ioctl

Currently in u_data_bridge driver, we are not handling the
TIOCM_CTS signal generared by SIO_IOCTL_INBOUND_FLOW IOCTL. Hence
we are not able to send BRK signal to the host and it keeps
sending data leading to data loss.
Fix this by handling TIOCM_CTS in the driver.

Change-Id: If8e4774e3e0772cb7189f3400d7e53e258b7d5a3
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>