net: ethernet: ti: am65-cpsw: avoid devm_alloc_etherdev, fix module removal

Usage of devm_alloc_etherdev_mqs() conflicts with
am65_cpsw_nuss_cleanup_ndev() as the same struct net_device instances
get unregistered twice. Switch to alloc_etherdev_mqs() and make sure
am65_cpsw_nuss_cleanup_ndev() unregisters and frees those net_device
instances properly.

With this, it is finally possible to rmmod the driver without oopsing
the kernel.

Fixes: 93a76530 ("net: ethernet: ti: introduce am65x/j721e gigabit eth subsystem driver")
Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Reviewed-by: Roger Quadros <roger@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>