ARM: imx: flexcan: Remove platform file

As there are no more users of the flexcan platform file, let's remove it.

Cc: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>