Since v1.5.0, dtc has been applying a heuristic to detect spi busses. It
erroneously thinks the spi node in at91sam9x5ek.dts defines a spi bus:

  ./arch/arm/dts/at91sam9x5ek.dts:25.9-29.7: Warning (spi_bus_bridge):
  	/ahb/apb/pinctrl@fffff400/spi: incorrect #address-cells for SPI bus
  ./arch/arm/dts/at91sam9x5ek.dts:25.9-29.7: Warning (spi_bus_bridge):
  	/ahb/apb/pinctrl@fffff400/spi: incorrect #size-cells for SPI bus
  ./arch/arm/dts/at91sam9x5ek.dtb: Warning (spi_bus_reg):
  	Failed prerequisite 'spi_bus_bridge'

Avoid this by renaming the node. While at it move the node to top-level
to reduce indentation.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>