pinctrl: lpc18xx: Use devm_pinctrl_register() for pinctrl registration

Use devm_pinctrl_register() for pin control registration.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Joachim Eastwood <manabian@gmail.com>
Acked-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>