Add nodes for devices used by PM code (mpu, dsp, iva).

Add a cpus node as well as recommended in the DT spec.

Remove mpu, dsp, iva devices init if is populated.
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Kevin Hilman <khilman@ti.com>