[nrf fromtree] boards: Enable adc node for nRF54H20 DK

Enables adc node to make it usable in tests/examples.

Signed-off-by: Karol Lasończyk <[email protected]>
(cherry picked from commit a04b2ad)

Author: kl-cruz

boards/nordic/nrf54h20dk/nrf54h20dk_nrf54h20_cpuapp.dts

@@ -289,3 +289,8 @@ zephyr_udc0: &usbhs {
 	pinctrl-names = "default", "sleep";
 	memory-regions = <&cpuapp_dma_region>;
 };
+
+&adc {
+	memory-regions = <&cpuapp_dma_region>;
+	status = "okay";
+};