i2c: imx: Add timer for handling the stop condition

Most IMX I2C interfaces don't generate an interrupt on a stop condition,
so it won't generate a timely stop event on a slave mode transfer.
Some users, like IPMB, need a timely stop event to work properly.

So, add a timer and add the proper handling to generate a stop event in
slave mode if the interface goes idle.

Signed-off-by: Corey Minyard <minyard@acm.org>
Tested-by: Andrew Manley <andrew.manley@sealingtech.com>
Reviewed-by: Andrew Manley <andrew.manley@sealingtech.com>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>