ARM: dts: msm: Declare stubs for /cpus and /soc nodes

Create stub declarations for the /cpus /soc nodes in the
arm/arm64 skeleton dtsi files. This will have the effect
of placing these nodes in front of the /chosen and /memory
nodes in the flattened DT blob. As a result, the /chosen
and /memory nodes will be placed near the end of the blob,
reducing the amount of memory that needs to be moved around
if these nodes need to be modified at boot time.

Change-Id: I5912e2dc81630b184401c5da0f6873386553f6f3
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>