MDIO: Kconfig: Specify more IPQ chipset supported

The IPQ MDIO driver currently supports the chipset IPQ40xx, IPQ807x,
IPQ60xx and IPQ50xx.

Add the compatible 'qcom,ipq5018-mdio' because of ethernet LDO dedicated
to the IPQ5018 platform.

Signed-off-by: Luo Jie <luoj@codeaurora.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>