omap: overo: Disable pull-ups on camera PCLK, HS and VS signals

The level shifters used on the Caspa camera module have a 4k output
impedance. Combined with the 100uA pull-up resistors in the OMAP3,
this raises the ground level to 400mV. Adding crosstalk between the
pixel clock and the HS/VS signals on the flat cable (a ground line in
between would have been nice), logic 0 levels can raise up to 650mV.
This exceeds the camera input pins VIL maximum voltage.  This change
suggested-by Laurent Pinchart

Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>