ARM: dts: at91: sama5d2: add I2S clock muxing nodes

This patch adds two clock muxes for the two I2S
buses present on sama5d2 platforms.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>