ARM: pxa: enhance smc91x platform data

Instead of having the smc91x driver relying on machine_is_*() calls,
provide this data through platform data, ie. idp, mainstone and
stargate.

This way, the driver doesn't need anymore machine_is_*() calls, which
wouldn't work anymore with a device-tree build.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>