sandbox: Enable more console options

Enable the pre-console buffer, displaying the model and post-relocation
console announce on sandbox. Also add a model name to the device tree.
This allows testing of these features.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Stephen Warren <swarren@nvidia.com>