smsc95xx: detect chip revision specific features

Instead of storing the number of wake-up frame filter registers
in the pdata structure, this patch changes the driver to detect
the type of device we have and store its available features.

The new two features will be used in future patches.

This patch is intended to have no change in behaviour.

Signed-off-by: Steve Glendinning <steve.glendinning@shawell.net>
Signed-off-by: David S. Miller <davem@davemloft.net>