ARM: imx: remove #ifdefery for unmerged flexcan driver

The flexcan driver was merged as e955cead.

Cc: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>