net: phy: realtek: add RTL8201F phy-id and functions

Add RTL8201F phy-id and the related functions to the driver.

The original patch is as follows:
https://patchwork.kernel.org/patch/2538341/

Signed-off-by: Jongsung Kim <neidhard.kim@lge.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>