amd-xgbe: Stop the PHY before releasing interrupts

Some configurations require the use of the hardware's MDIO support to
communicate with external PHYs. The MDIO commands indicate completion
through the device interrupt. When bringing down the device the interrupts
were released before stopping the external PHY, resulting in MDIO command
timeouts. Move the stopping of the PHY to before the releasing of the
interrupts.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>