net: smc91x: use io{read, write}*_rep accessors instead of string functions

The {read,write}s{b,w,l} operations are not defined by all architectures
and are being removed from the asm-generic/io.h interface.

This patch replaces the usage of these string functions in the default
SMC accessors with io{read,write}{8,16,32}_rep calls instead, which are
defined for all architectures.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ben Herrenschmidt <benh@kernel.crashing.org>
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>