phy: marvell: phy-mvebu-cp110-comphy: Rename HS-SGMMI to 2500Base-X

Comphy phy mode 0x3 is incorrectly named. It is not SGMII but rather
2500Base-X mode which runs at 3.125 Gbps speed.

Rename macro names and comments to 2500Base-X.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: eb6a1fcb ("phy: mvebu-cp110-comphy: Add SMC call support")
Fixes: c2afb2fe ("phy: mvebu-cp110-comphy: Rename the macro handling only Ethernet modes")
Signed-off-by: David S. Miller <davem@davemloft.net>