dm: sandbox: Add driver-model block-device support for sandbox

Update the host driver to support driver model for block devices. A future
commit will remove the old code, but for now it is useful to be able to use
it both with and without CONFIG_BLK.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Stephen Warren <swarren@nvidia.com>
3 files changed