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>

test/py/tests/vboot/sandbox-u-boot.dts

@@ -4,6 +4,9 @@
 	model = "Sandbox Verified Boot Test";
 	compatible = "sandbox";
 
+	binman {
+	};
+
 	reset@0 {
 		compatible = "sandbox,reset";
 	};