pinctrl: samsung: Replace syscore ops with standard platform device pm_ops

Once the dependency on PMU driver (for pad retention control) has been
removed, there is no reason to use syscore_ops based suspend/resume.
This patch replaces it with standard platform device pm_ops based solution.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>