phy: marvell: phy-mvebu-cp110-comphy: add support for 5gbase-r

Add support for PHY_INTERFACE_MODE_5GBASER mode within the Marvell CP110
common PHY driver.

This is currently only supported via SMC calls to TF-A. Legacy support
may be added later, if needed.

Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>