dts: arm: move SoC dtsi into per vendor dir

Move the SoC dtsi into a vendor dir so as we grow and possibly share
things with other projects we are hopefully in sync (or closer to it).

Change-Id: I71666cff49f9694eee3f5d92dac8aeea416b730a
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>