net: phy: mdio-gpio: Cut surplus includes

The GPIO MDIO driver now needs only <linux/gpio/consumer.h>
so cut the legacy <linux/gpio.h> and <linux/of_gpio.h>
includes that are no longer used.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>