sandbox: enable cros-ec-keyb in test.dtb

Currently keyboard input fails in the GUI window opened by

    ./u-boot -T -l

Add the missing include to test.dts.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index 2600360..f15d1eb 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -1402,3 +1402,4 @@
 };
 
 #include "sandbox_pmic.dtsi"
+#include "cros-ec-keyboard.dtsi"