ARM: dts: at91: sama5d2: add nodes for I2S controllers

This patch adds DT nodes for I2S0 and I2S1. It also adds an alias for
each I2S node.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
[codrin.ciubotariu@microchip.com: removed unnecessary clock phandles]
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>