phylib: Add Clause 45 read/write functions

Need an extra parameter to read or write Clause 45 PHYs, so
need a different API with the extra parameter.

Signed-off-by: Andy Fleming <afleming@gmail.com>
Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>