net: dsa: microchip: parse PHY config from device tree

net: dsa: microchip: parse PHY config from device tree

Introduce ksz_parse_dt_phy_config() to validate and parse PHY
configuration from the device tree for KSZ switches. This function
ensures proper setup of internal PHYs by checking `phy-handle`
properties, verifying expected PHY IDs, and handling parent node
mismatches. Sets the PHY mask on the MII bus if validation is
successful. Returns -EINVAL on configuration errors.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20241106075942.1636998-7-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>