sandbox: Use the reset driver to handle reset

Move sandbox over to use the reset uclass for reset, instead of a direct
call to do_reset(). This allows us to add tests.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/misc/reset_sandbox.c b/drivers/misc/reset_sandbox.c
index 3cc61ed..917121b 100644
--- a/drivers/misc/reset_sandbox.c
+++ b/drivers/misc/reset_sandbox.c
@@ -51,7 +51,7 @@
 		state->last_reset = type;
 		if (!state->reset_allowed[type])
 			return -EACCES;
-		/* TODO: sandbox_exit(); */
+		sandbox_exit();
 		break;
 	default:
 		return -ENOSYS;