Move the definition of DM64XX_VDD3P3V_PWDN from hardware.h
to devices.c since it is used only there.

This also helps rid hardware.h of platform private stuff.
Signed-off-by: NManjunath Hadli <manjunath.hadli@ti.com>
Signed-off-by: NSekhar Nori <nsekhar@ti.com>