net: phy: Don't register LEDs for genphy

In the Linux kernel, the following vulnerability has been resolved:

net: phy: Don't register LEDs for genphy

If a PHY has no driver, the genphy driver is probed/removed directly in

phy_attach/detach. If the PHY's ofnode has an "leds" subnode, then the

LEDs will be (un)registered when probing/removing the genphy driver.

This could occur if the leds are for a non-generic driver that isn't

loaded for whatever reason. Synchronously removing the PHY device in

phy_detach leads to the following deadlock:

rtnl_lock()

ndo_close()

...

phy_detach()

phy_remove()

phy_leds_unregister()

led_classdev_unregister()

led_trigger_set()

netdev_trigger_deactivate()

unregister_netdevice_notifier()

rtnl_lock()

There is a corresponding deadlock on the open/register side of things

(and that one is reported by lockdep), but it requires a race while this

one is deterministic.

Generic PHYs do not support LEDs anyway, so don't bother registering

them.