ARM: dts: Add SYSREG block node for S5P/Exynos4 SoC series

This patch adds device tree node for the SYSREG registers block
found in Samsung S5P/Exynos SoC series. The SYSREG module
generates control signals for the ARM CPU and various IP blocks
and buses. SYSREG block registers are exposed through APB bus
interface. A sysreg device tree node is to be associated with
mfd syscon driver and all SYSREG clients should use regmap
interface it provides. It allows to eliminate any possible races
and conflicts should different drivers attempt to concurrently
access same register.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>