firmware: Allow firmwares to provide next mode and options

This patch extends existing firmwares (i.e. fw_jump and fw_payload)
to explicitly provide next mode and options to fw_base.

We also introduce fw_save_info() which is called by fw_base very
early on boot HART. This function can be used by existing firmwares
(i.e. fw_jump and fw_payload) to save information passed by previous
booting stage.

Overall, this is a preparatory patch for implementing fw_dynamic.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>