pinctrl: samsung: Move retention control from mach-exynos to the pinctrl driver

This patch moves pad retention control from PMU driver to Exynos pin
controller driver. This helps to avoid possible ordering and logical
dependencies between machine, PMU and pin control code. Till now it
worked fine only because sys_ops for PMU and pin controller were called
in registration order.
This is also a preparation for adding new features to Exynos pin
controller driver, like runtime power management and suspending
individual pin controllers, which might be a part of some power domain.

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>