net: phy: micrel: add coma mode GPIO

The LAN8814 has a coma mode pin which puts the PHY into isolate and
power-dowm mode. Unfortunately, the mode cannot be disabled by a
register. Usually, the input pin has a pull-up and connected to a GPIO
which can then be used to disable the mode. Try to get the GPIO and
deassert it.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>