defxx: Disable DEFEA's ESIC I/O decoding on shutdown

Make sure the option card does not respond after shutdown by disabling
it via ESIC's Expansion Board Control register.  Also disable memory and
port I/O decoders, the latter in particular to disable slot-specific I/O
decoding that otherwise remains active even in the board is disabled.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>