ARM: at91/dt: disable pull-up on vbus-gpio (PB16) to reduce power consumption

There is an external resistor divider on PB16, acting like a pull-down,
the pull-up increase power consumption and prevent the vbus detect pin
to reach Vss voltage, ~1.5V mesured on my board, it might not even work
if the pull-up is stronger than usual.

Signed-off-by: Sylvain Rochet <sylvain.rochet@finsecur.com>
Acked-by: Bo Shen <voice.shen@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>