uefi: Refactor the fwdb/storage setup so it can be used outside of vboot.

The network boot version of depthcharge doesn't need to set up RO/RW vboot
storage areas, but it does need to set up storage for the netboot params.
This makes the code usable by netboot.

Change-Id: Ia55dac70c727889e332ea3e2b91dbe225949dd1c
3 files changed