arm64: dts: salvator-x: populate EXTALR

It can be used for the watchdog.
Signed-off-by: NWolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

arch/arm64/boot/dts/renesas/r8a7795-salvator-x.dts

@@ -141,6 +141,10 @@
 	clock-frequency = <16666666>;
 };
 
+&extalr_clk {
+	clock-frequency = <32768>;
+};
+
 &pfc {
 	pinctrl-0 = <&scif_clk_pins>;
 	pinctrl-names = "default";