Supporting eeproms from device-tree in FruDevice

[Patrick Venture]

I'm nearly done adapting FruDevice to handle FRUs that have drivers
ready, and raw i2c FRUs.  Before I push the code for review, I wanted
to get early feedback on the design change.  I wanted to keep it small
and surgical.

Basically, for each bus, before it scans for FRUs raw, it searches for
eeprom files for that bus.  And validates, and adds those devices.
Those addresses go into a skip list, and another list (used elsewhere
for writes).  The normal get frus code is then run but it'll skip the
addresses already handled.  Elsewhere, the code that handles writes to
the FRUs will check to see if the bus/address is in the list of
"driver handled" ones, and if so it'll call to write via the eeprom
file instead of the raw i2c commands.

Basically, the new code wouldn't interfere with normal operations, but
just extend it to leverage a driver when it's available.

Patrick