serial: qcom-geni: Enable support for half-duplex mode

serial: qcom-geni: Enable support for half-duplex mode

Enable the use of the RTS pin for direction control in half-duplex modes to
prevent data collisions. Utilize the rs485 structure and callbacks in the
serial core framework to support half-duplex modes. Implement support for
the TIOCSRS485 IOCTL value and the struct serial_rs485.

Signed-off-by: Anup Kulkarni <quic_anupkulk@quicinc.com>
Link: https://lore.kernel.org/r/20250603110145.3835111-1-quic_anupkulk@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>