net: phy: microchip: document where the LAN88xx PHYs are used

net: phy: microchip: document where the LAN88xx PHYs are used

The driver uses the name LAN88xx for PHYs with phy_id = 0x0007c132. But
with this placeholder name no documentation can be found on the net.

Document the fact that these PHYs are build into the LAN7800 and LAN7850
USB/Ethernet controllers.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250515082051.2644450-1-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>