[SCSI] libsas: Add an LU reset mechanism to the error handler

After discussion with andmike and dougg, it seems that the purpose of
eh_device_reset_handler is to issue LU resets, and that
eh_bus_reset_handler would be a more appropriate place for a phy reset.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>