arm64: dts: r8a7796: salvator-x: Populate EXTALR

It can be used for the watchdog.

Based on similar work for r8a7795/salvator-x by Wolfram Sang.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

arch/arm64/boot/dts/renesas/r8a7796-salvator-x.dts

@@ -49,6 +49,10 @@
 	clock-frequency = <16666666>;
 };
 
+&extalr_clk {
+	clock-frequency = <32768>;
+};
+
 &scif2 {
 	pinctrl-0 = <&scif2_pins>;
 	pinctrl-names = "default";