can: flexcan: add platform data header

Add platform data header for flexcan.

Link: https://lore.kernel.org/r/20210702094841.327679-1-angelo@kernel-space.org
Signed-off-by: Angelo Dureghello <angelo@kernel-space.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>