ARM: imx: prepare for removal of flexcan_platform_data

As there are no imx in-tree users of flexcan_platform_data, this patch removes
the possibility to register a flexcan device with platform data.

The functionality to swith on/off CAN transceivers is added to DT via
regulators in a later patch.

Compile time tested with imx_v4_v5_defconfig and imx_v6_v7_defconfig.

Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>