ARM: dts: exynos: Remove Exynos5440

The Exynos5440 (quad-core A15 with GMAC, PCIe, SATA) was targeting
server platforms but it did not make it to the market really.  There are
no development boards with it and probably there are no real products
neither.  The development for Exynos5440 ended in 2013 and since then
the platform is in maintenance mode.

Remove all Device Tree sources for Exynos5440, as first step of removal
of the platform to simplify the code and drivers.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Andi Shyti <andi@etezian.org>
Reviewed-by: Rob Herring <robh@kernel.org>