powerpc/fsl: proliferate simple-bus compatibility to soc nodes

add simple-bus compatible property to soc nodes for 83xx/85xx platforms
that were missing them.  Add same to platform probe code.

This fixes SoC device drivers (such as talitos) to succeed in matching
devices present in the soc node.

also update mpc836x_rdk dts to new SEC bindings (overlooked in commit
3fd44736

: powerpc/fsl: update crypto node definition and device tree
instances).

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>