soc: qcom: cmd-db: adjust probe for U-Boot

soc: qcom: cmd-db: adjust probe for U-Boot

Integrate cmd-db into the U-Boot driver model.

This is just a wrapper around an in-memory database, so we just need to
get the address and validate that cmd-db is there.

Since cmd_db_header will be stored in the .data section we can skip
bind if it's already set.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>