omap4460: fix TPS initialization

TPS power IC is controlled using a GPIO (gpio_wk7).
This GPIO should be maintained at logic 1 always. As
such an internal pull-up on this pin will do the job,
driving the GPIO outuput is not needed. This will avoid
the need of using GPIO library in SPL and also may
save some power.

Signed-off-by: Aneesh V <aneesh@ti.com>