sandbox: Enable devres subsystem

This should be used for sandbox. We can convert at least one driver to use
it, but in the meantime, enable the feature so that the code is
build-tested.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index e6a4590..874a26b 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -53,3 +53,4 @@
 CONFIG_LED_GPIO=y
 CONFIG_SYSCON=y
 CONFIG_REGMAP=y
+CONFIG_DEVRES=y