sandbox: Add a build without CMDLINE

Sometimes this breaks, so add a build to keep it working. Since sandbox
enables a lot of options, it is a good board to use. The new config is
created simply by copying the existing sandbox and turning off CMDLINE

Once we have tests for non-CMDLINE operation, this can be adjusted to
run those tests.

Create a new build which will be picked up by CI. Update the maintainer
entry as well.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 0399ed1..452ec44 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1551,6 +1551,7 @@
 M:	Simon Glass <sjg@chromium.org>
 S:	Maintained
 F:	arch/sandbox/
+F:	configs/sandbox*
 F:	doc/arch/sandbox.rst
 F:	drivers/*/*sandbox*.c
 F:	include/dt-bindings/*/sandbox*.h