Uploading firmware in-band

[Patrick Venture]

I've pushed this for comments,
https://gerrit.openbmc-project.xyz/#/c/9497/1 - it's the BMC-side of
our implementation for receiving the BMC image.  It supports LPC, PCI,
and in-band IPMI as a transport mechanism.  it doesn't dig into the
signature stuff or the flashing portions, however it does assume there
is a signature verification service, and can receive the signature
itself.

Regards,
Patrick