ARM: dts: at91: sama5d2_xplained: fix QSPI0 node

Fix the following:
- use "jedec,spi-nor" binding, we use jedec compatible flashes
- set bus width to 4, we use quad capable flashes
- differentiate bewteen data and clk and cs pins
- drop partions as we don't use them in u-boot.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@microchip.com>
[tudor.ambarus@microchip.com: use "jedec,spi-nor", edit commit message]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>