fix(drivers/marvell/comphy): fix name of 3.125G SerDes mode

There is no support for 2.5/3.125G SGMII. This 3.125G SerDes mode is not
SGMII. It is just plain 1000Base-X (as defined in IEEE 802.3z standard)
but upclocked 2.5x. This mode is commonly known under name 2500Base-X.

So remove incorrect SGMII keyword from names and comments and replace it
by more adequate 2500Base-X keyword.

There is no functional change in code, just renaming macros and updating
comments.

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: If79aec16cc233f4896aafd75bfbbebb3f172a197
4 files changed