ARM: OMAP2+: Fix voltage scaling init for device tree

We are currently disabling the init of voltage scaling
for device tree. With the voltage scaling problems fixed
for omap3 in general, there's no need to disable the voltage
scaling init for device tree based booting.

Cc: Kevin Hilman <khilman@linaro.org>
Cc: Nishanth Menon <nm@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>