ARM: dts: imx6ul: Add SAI alias

Add SAI alias entries, which makes it possibe for the SAI driver
to retrieve the port instance.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6ul.dtsi

@@ -36,6 +36,9 @@
 		serial5 = &uart6;
 		serial6 = &uart7;
 		serial7 = &uart8;
+		sai1 = &sai1;
+		sai2 = &sai2;
+		sai3 = &sai3;
 		spi0 = &ecspi1;
 		spi1 = &ecspi2;
 		spi2 = &ecspi3;