net: stmmac: dwmac-rk: Don't set the regulator voltage for phy from the driver

As these settings can be directly expressed from devicetree for both fixed
regulators and pmic-integrated regulators, it is more standard to set them
from dts and let the regulator framework use the right voltage informations
when it is used in the driver.

Signed-off-by: Romain Perier <romain.perier@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: David S. Miller <davem@davemloft.net>