ARM: dts: exynos: Move common nodes to exynos5.dtsi

Exynos5420 and Exynos5250 share some nodes: the PWM, syscon
(sysreg_system_controller) and first four I2C controllers. Move them to
parent DTSI to avoid duplication.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>