RAID event support.

This will hot add and remove raid volumes
when managment application creates and
deletes the volumes.  The driver is basically
responding to firmware asyn events, and reporting
the changes to the above layers.
Signed-off-by: NEric Moore <Eric.Moore@lsil.com>
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>