If the MEM-AP cache is invalid, don't display it; just report that
invalidity as an error.  (This bug has been observed with "mdw 0 32"
after just a "reset halt".  Some code is being wrongly bypassed...)

If it's valid, display that cache at DEBUG level, not ERROR.  Also,
don't assume it's an AHB-AP; it could be another flavor of MEM-AP.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>