ARM: dts: add pwm DT nodes to Exynos5250 and Exynos5420

Add the device-tree binding for the PWM controller to Exynos5250 and Exynos5420

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Olof Johansson <olofj@chromium.org>
Signed-off-by: Leela Krishna Amudala <l.krishna@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>