serdev: implement get/set tiocm

Add method for getting and setting tiocm.

Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
3 files changed