net: phy: micrel: add cable test support for KSZ9477-class PHYs

Enable cable test support for KSZ9477-class PHYs by reusing the
existing KSZ9131 implementation.

This also adds support for 100Mbit-only PHYs like KSZ8563, which are
identified as KSZ9477. For these PHYs, only two wire pairs (A and B)
are active, so the cable test logic limits the pair_mask accordingly.

Support for KSZ8563 is untested but added based on its register
compatibility and PHY ID match.

Tested on KSZ9893 (Gigabit): open and short conditions were correctly
detected on all four pairs. Fault length reporting is functional and
varies by pair. For example:
- 2m cable: open faults reported ~1.2m (pairs B–D), 0.0m (pair A)
- No cable: all pairs report 0.0m fault length

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250610091354.4060454-4-o.rempel@pengutronix.de


Signed-off-by: Jakub Kicinski <kuba@kernel.org>