sandbox: Use the generic VPL option to enable VPL

Avoid using CONFIG_SANDBOX_VPL since we have a generic option which works
just as well.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/sandbox.dts b/arch/sandbox/dts/sandbox.dts
index e9b6745..12d3eff 100644
--- a/arch/sandbox/dts/sandbox.dts
+++ b/arch/sandbox/dts/sandbox.dts
@@ -103,6 +103,6 @@
 #include "cros-ec-keyboard.dtsi"
 #include "sandbox_pmic.dtsi"
 
-#ifdef CONFIG_SANDBOX_VPL
+#if IS_ENABLED(CONFIG_SUPPORT_VPL)
 #include "sandbox_vpl.dtsi"
 #endif