ARM: dts: at91: sama5d2: add missing flexcom spi node properties

SPI nodes require #address-cells and #size-cells add those properties in
the flexcom spi nodes.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20200831171129.3886857-8-alexandre.belloni@bootlin.com