realtek: Add specific PHY polling options to support the Zyxel XGS1250/XGS1210

Both the Aquantia AQR113c and the RTL8226 PHYs in the Zyxel XGS1250 and the
Zyxel XGS1210 require special polling configuration settings in the
RTL930X_SMI_10GPHY_POLLING_REGxx_CFG configuration registers. Set them.
Additionally, for RTL 1GBit phys set the RTL930X_SMI_PRVTE_POLLING_CTRL bits
in the poll mask.

Signed-off-by: Birger Koblitz <git@birger-koblitz.de>