ARM: dts: msm8916: add "simple-bus" compat string to soc-node

Reparent memory mapped devices from soc-node to root-node
and remove explicit call to of_platform_populate for
the soc-node.

Change-Id: Ia7dc30dbbbb14d6524ac361c669baf69d45e3761
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>