phy/micrel: Implement support for KSZ8021

The KSZ8021 PHY was previously caught by KS8051, which is not correct.
This PHY needs additional setup if it is strapped for address 0. In such
case an reserved bit must be written in the 0x16, "Operation Mode Strap
Override" register. According to the KS8051 datasheet, that bit means
"PHY Address 0 in non-broadcast" and it indeed behaves as such on KSZ8021.
The issue where the ethernet controller (Freescale FEC) did not communicate
with network is fixed by writing this bit as 1.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: David J. Choi <david.choi@micrel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>