net: phy: micrel: disable NAND-tree for KSZ8051

NAND-tree is used to check wiring between MAC and PHY using NAND gates
on the PHY side, hence the name.

NAND-tree initial status is latched at reset by probing the IRQ pin.
However some devices are sharing the PHY IRQ pin with other peripherals
such as Atmel SAMA5D[34]x-EK boards when using the optional TM7000
display module, therefore they are switching the PHY in NAND-tree test
mode depending on the current IRQ line status at reset.

This patch ensure PHY is not in NAND-tree test mode only for the Micrel
KSZ8051 PHY used by Atmel. There are other Micrel PHY affected but I
doubt they are used on such weird hardware design.

Signed-off-by: Sylvain Rochet <sylvain.rochet@finsecur.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>