ARM: imx: pwm: Add support for MX53

Instead of adding the check for MX53 CPU type, use the negative logic and let
PWM to be configured for MX53 as well.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>