net: mdio-gpio: Convert to use gpiod functions where possible

Using gpiod functions lets us use functionality which is not available
with gpio functions.

There is no gpiod function to match devm_gpio_request_one, so leave it
in place and use gpio_to_desc() to convert absolute pin numbers to gpio
descriptors.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>