ARM: OMAP3+: do not register non-dt OPP tables for device tree boot

OMAP3+ supports both device tree and non-device tree boot.
Device tree bindings for OMAP3+ is supposed to be added via dts following:
Documentation/devicetree/bindings/power/opp.txt

Since we now have device tree entries for OMAP3+ cpu OPPs,
The current code wrongly adds duplicate OPPs. So, dont register OPPs
when booting using device tree.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>