ipmi: provide support for FRUs

ipmi: provide support for FRUs

This patch provides a simple FRU support for the BMC simulator. FRUs
are loaded from a file which name is specified in the object
properties, each entry having a fixed size, also specified in the
properties. If the file is unknown or not accessible for some reason,
a unique entry of 1024 bytes is created as a default. Just enough to
start some simulation.

These commands complies with the IPMI spec : "34. FRU Inventory Device
Commands".

Signed-off-by: Cédric Le Goater <[email protected]>
Acked-by: Corey Minyard <[email protected]>
[dwg: Folded in subsequent fix to handle NULL filename]
Signed-off-by: David Gibson <[email protected]>