ARM: EXYNOS: Add support for EXYNOS5420 SoC

EXYNOS5420 is new SoC in Samsung's Exynos5 SoC series. Add
initial support for this new SoC.

Signed-off-by: Chander Kashyap <chander.kashyap@linaro.org>
Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>