can: flexcan: Use SIMPLE_DEV_PM_OPS

Using SIMPLE_DEV_PM_OPS can make the code smaller and simpler.

Also change CONFIG_PM to CONFIG_PM_SLEEP.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>