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

Currently in f_cdev 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>
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>