test: add sandbox timer to test.dts

Add missing sandbox timer to test.dts, so that test-dm works.
Signed-off-by: NThomas Chou <thomas@wytron.com.tw>
Acked-by: NSimon Glass <sjg@chromium.org>
Tested-by: NSimon Glass <sjg@chromium.org>

arch/sandbox/dts/test.dts

@@ -279,6 +279,11 @@
 			0x38 8>;
 	};
 
+	timer {
+		compatible = "sandbox,timer";
+		clock-frequency = <1000000>;
+	};
+
 	uart0: serial {
 		compatible = "sandbox,serial";
 		u-boot,dm-pre-reloc;