ARM: dts: exynos: split dmas into array of phandles in Exynos5250

"dmas" property should be rather an array of phandles, as dtschema
points.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Andi Shyti <andi@etezian.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Link: https://lore.kernel.org/r/20220120175747.43403-2-krzysztof.kozlowski@canonical.com