pinctrl: exynos: Add pinctrl support for Exynos850

Add pinctrl support for Exynos850 SoC. It was mostly extracted from
corresponding Linux kernel code [1]. Power down modes and external
interrupt data were removed while converting the code for U-Boot, but
everything else was kept almost unchanged.

[1] drivers/pinctrl/samsung/pinctrl-exynos-arm64.c

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Chanho Park <chanho61.park@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>