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

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

Keep the header pointer in the .data section so we don't initialize it
again after relocation, adjust cmd_db_get_header() to work with the
U-Boot API, and skip validating the header since all cmd-db users are
children of the rpmh-rsc and those children will only probe if cmd-db
initializes successfully.

Acked-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>