arch/tile: allow querying cpu module information from the hypervisor

This just adds a few more attributes to the information Linux
can query from the hypervisor for the /sys/hypervisor/board/ directory,
providing part, serial#, revision#, and description for cpu modules
(as opposed to the board itself, or any mezzanine boards).

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>