ARM: dts: omap4-panda: Fix DVI EDID reads

On Panda the +5V supply for DVI EDID is supplied by the
same regulator that poweres the USB Hub. Currently, the
DSS/DVI subsystem doesn't know how to manage this regulator
and so DVI EDID reads will fail if USB Hub is not enabled.

As a temporary fix we keep this regulator permanently enabled
on boot. This fixes the DVI EDID read problem.

CC: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>