smc91x: SMC_IO_SHIFT platform data support for default case

Commit 15919886 added SMC_IO_SHIFT
platform data support. After that ARM board support was added.

The default case is still missing though, so on SuperH SMC_IO_SHIFT
is constantly zero regardless of what you pass as platform data.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Test-by: Luca Santini <luca.santini@spesonline.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>