ARM: OMAP2+: pm: Do not init statically the SR and voltage layer with DT

In the case of DT, the PMIC and SR initialization will be done using
a completely different mechanism.

Disable this part if a DT blob is available.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Acked-by: Kevin Hilman <khilman@ti.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>