u-boot mirroring support

Design is at the link below.
https://gerrit.openbmc.org/c/openbmc/docs/+/58025

Tested:
  Tested all "Test Scenarios" specified in the design.

Signed-off-by: Lakshmi Yadlapati <lakshmiy@us.ibm.com>
Change-Id: I064115ee1e966a0a1b3ce7ec246c1f88f0bd87f7
4 files changed