boards: nordic: nRF54L15DK: set HFXO clock latency to 854

The HFXO used on nRF54L15 DK has the typical startup latency of 854us.

Signed-off-by: Rafał Kuźnia <rafal.kuznia@nordicsemi.no>

Author: e-rk

boards/nordic/nrf54l15dk/nrf54l15dk_common.dtsi

@@ -108,5 +108,9 @@
 	pinctrl-names = "default", "sleep";
 };
 
+&hfxo {
+	startup-time-us = <854>;
+};
+
 /* Get a node label for wi-fi spi to use in shield files */
 wifi_spi: &spi22 {};