smc91x: remove isa stuff from smc91x driver

ISA support in smc91x is incomplete. I doubt there're any smc91x isa card.
This driver is greatly used on arm pxa platforms. Hence we remove the
isa stuff from smc91x driver.

Signed-off-by: Luotao Fu <lfu@pengutronix.de>
Acked-by: Steve Glendinning <steve.glendinning@smsc.com>
Signed-off-by: David S. Miller <davem@davemloft.net>