Work-around to temporarily support older PROMs with new flush device code.

This code allows systems running older PROMs to continue to run on the new
kernel base until a new official PROM is released.
Signed-off-by: Prarit Bhargava <prarit@sgi.com>
Acked-by: Jes Sorensen <jes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>