i2c: imx: Synthesize end of transaction events without idle interrupts

Only the Layerscape SoCs have interrupts on bus idle, which facilitate
sending events which complete slave bus transactions.

Add support for synthesizing missing events. If we see a master request,
or a newly addressed slave request, if the last event sent to the backend
was I2C_SLAVE_READ_REQUESTED, send the backend a I2C_SLAVE_READ_PROCESSED
followed by I2C_SLAVE_STOP. For all other events, send an I2C_SLAVE_STOP.

Signed-off-by: Kevin Paul Herbert <kph@platinasystems.com>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>