ARM: dts: exynos: Remove unneeded address/size cells in Exynos5260 GIC

The Exynos5260 GIC node does not have any children so remove the address
and size cells as they are not needed by DT bindings.  The size-cells of
'0' were also incorrect.  This fixes dtbs_check warning:

  arch/arm/boot/dts/exynos5260-xyref5260.dt.yaml: interrupt-controller@10481000: #size-cells:0:0: 1 was expected

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200901075417.22481-4-krzk@kernel.org