ARM: dts: at91: sama5d2_xplained: remove pull-up on SD/MMC lines

As the board have the proper pull-ups soldered on the data and CMD
lines we don't need them specified in the PADs. So remove the
"bias-pull-up" property and set "bias-disable".
This will also save some power.

Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
[claudiu.beznea@microchip.com: change subject to match the desired prefix]
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>