ARM: dts: ux500: Push VMMCI down to each tree

The setting of VMMCI differs so much between different
boards that we need to handle it on a per-board basis
rather that complicating things by overriding stuff from
the included DTSI:s. Push it down into top-level tree
instead.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>