phy: lynx-10g: fix bugs in 'fsl,ls1088a-serdes1' and mark it as tested

commit  0392c61d9eb5cb56fa0a3f334b28fb82e278c734 from
https://github.com/nxp-imx/linux-imx lf-6.1.y

Fix the following bugs in the 'fsl,ls1088a-serdes1':
- Remove the LANE_MODE_2500BASEX mode since this is not listed in the
SoC RM as a support mode.
- Mark the XFI protocol converter as being available on lanes #2 and #3.
- Remove a forgotten 'return' statement from the
ls1088a_serdes1_get_pcvt_offset() function.

This driver was tested on the LS1088ARDB board with the following
protocols: 10GBASER, 1000BASE-X/SGMII and QSGMII. As such, mark the SoC
as tested.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>