net: dsa: felix: don't use devres for mdiobus

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

net: dsa: felix: don't use devres for mdiobus

As explained in commits:

74b6d7d13307 ("net: dsa: realtek: register the MDIO bus under devres")

5135e96a3dd2 ("net: dsa: don't allocate the slave_mii_bus using devres")

mdiobus_free() will panic when called from devm_mdiobus_free() <-

devres_release_all() <- __device_release_driver(), and that mdiobus was

not previously unregistered.

The Felix VSC9959 switch is a PCI device, so the initial set of

constraints that I thought would cause this (I2C or SPI buses which call

->remove on ->shutdown) do not apply. But there is one more which

applies here.

If the DSA master itself is on a bus that calls ->remove from ->shutdown

(like dpaa2-eth, which is on the fsl-mc bus), there is a device link

between the switch and the DSA master, and device_links_unbind_consumers()

will unbind the felix switch driver on shutdown.

So the same treatment must be applied to all DSA switch drivers, which

is: either use devres for both the mdiobus allocation and registration,

or don't use devres at all.

The felix driver has the code structure in place for orderly mdiobus

removal, so just replace devm_mdiobus_alloc_size() with the non-devres

variant, and add manual free where necessary, to ensure that we don't

let devres free a still-registered bus.