arch: Kconfig: imply BINMAN for SANDBOX

To be able to use the tool binman on sandbox,
the config SANDBOX should imply BINMAN.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/arch/sandbox/dts/sandbox.dtsi b/arch/sandbox/dts/sandbox.dtsi
index 66b813f..826db26 100644
--- a/arch/sandbox/dts/sandbox.dtsi
+++ b/arch/sandbox/dts/sandbox.dtsi
@@ -7,6 +7,9 @@
 #define USB_CLASS_HUB			9
 
 / {
+	binman {
+	};
+
 	chosen {
 		stdout-path = "/serial";
 	};