pinctrl: spear: 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: Viresh Kumar <vireshk@kernel.org>
Cc: spear-devel@list.st.com
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>