phy: Add Sparx5 ethernet serdes PHY driver

Add the Microchip Sparx5 ethernet serdes PHY driver for the 6G, 10G and 25G
interfaces available in the Sparx5 SoC.

Signed-off-by: Bjarni Jonasson <bjarni.jonasson@microchip.com>
Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210218161451.3489955-4-steen.hegelund@microchip.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>