commit 9b00b300 upstream.

In flexcan_chip_enable() and flexcan_chip_disable() fixed delays are used.
Experiments have shown that the transition from and to low power mode may take
several microseconds.

This patch adds a while loop which polls the Low Power Mode ACK bit (LPM_ACK)
that indicates a successfull mode change. If the function runs into a timeout a
error value is returned.
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>