phy: lynx-28g: add support for 25GBASER

phy: lynx-28g: add support for 25GBASER

Add support for 25GBASE-R in the Lynx 28G SerDes PHY driver. This will
be used by the dpaa2-mac consumer on LX2160A with:
- phy_validate(phy, PHY_MODE_ETHERNET, PHY_INTERFACE_MODE_25GBASER) to
  detect support.
- phy_set_mode_ext(phy, PHY_MODE_ETHERNET, PHY_INTERFACE_MODE_25GBASER)
  to reconfigure the lane for this protocol.

The intended use case for dynamic protocol switching to 25GBase-R is
with SFP28 modules, and protocol switching is triggered by the SFP
module insertion. There also exists a 25GBase-KR use case, where the
protocol switching is covered by IEEE 802.3 clause 73 auto-negotiation.
However, that is not handled here; it merely needs the support added
here as basic ground work.

The lane frequency for 25GbE is sourced from a clock net frequency of
12.890625 GHz, as produced by PLLF or PLLS, further multiplied by the
lane by 2. The clock net frequencies produced by the PLLs are treated as
read-only by the driver, so the absence of a PLL provisioned for the
right clock net frequency implies absence of 25GbE support, even though
a lane might have the appropriate protocol converter for it.

In terms of implementation, the change consists of:
- determining at probe time if any PLL was preconfigured for the
  required clock net frequency for 25GbE
- adding the default lane parameters for reconfiguring a lane to 25GbE
  irrespective of the original protocol
- allowing this operating mode only on supported lanes, i.e. all lanes
  of LX2162A SerDes #1, and LX2160A SerDes lanes 0-1, 4-7.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Josua Mayer <josua@solid-run.com>
Link: https://patch.msgid.link/20260511150023.1903577-6-vladimir.oltean@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>