net: w5100: support W5200

This adds support for W5200 chip.

W5100 and W5200 have similar memory map although some of their offsets
are different.  The register access sequences between them are different
but w5100 driver has abstraction layer for difference bus interface
modes so it is easy to add W5200 support to w5100 and w5100-spi drivers.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Mike Sinkovsky <msink@permonline.ru>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>