net: libwx: add phylink to libwx

For the following implementation, add struct phylink and phylink_config
to wx structure. Add the helper function for converting phylink to wx,
implement ethtool ksetting and nway reset in libwx.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>