pinctrl: imx: Use devm_pinctrl_register() for pinctrl registration

Use devm_pinctrl_register() for pin control registration and remove
need of .remove callback.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Stefan Agner <stefan@agner.ch>
Cc: Adrian Alonso <aalonso@freescale.com>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>