ARM: dts: exynos: Remove unsupported s2mps11 regulator bindings from Exynos5420 boards

The bindings like s2mps11,buck6-ramp-enable or s2mps11,buck2-ramp-delay
were ignored. They were never parsed by s2mps11 regulator driver. Also
the values used in these bindings were equal to default reset values of
S2MPS11 device. It is safe to remove them.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>