sandbox: defconfig: enable CONFIG_SM option

We use this option to test UCLASS_SM.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/r/20230921081346.22157-6-avromanov@salutedevices.com


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>