net: phy: realtek: rename RTL8211F_PAGE_SELECT to RTL821x_PAGE_SELECT

This renames the definition of page select register from
RTL8211F_PAGE_SELECT to RTL821x_PAGE_SELECT to use it across models.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>