ARM: dts: update watchdog device nodes for exynos5250 and exynos5420

ARM: dts: update watchdog device nodes for exynos5250 and exynos5420

In EXYNOS5 series SoCs, PMU has registers to enable/disable mask/unmask
watchdog timer which is not the case with s3c series SoCs so, there is a
need to have different compatible names for watchdog to handle these pmu
registers access.

Hence this patch removes watchdog node from Exynos5.dtsi common file and
make it separate by updating existing node in Exynos5250 and adding new node
to Exynos5420. This patch also makes the watchdog node enabled by default

Signed-off-by: Leela Krishna Amudala <l.krishna@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>