net: stmmac: dwc-qos: Split out ->probe() and ->remove()

Split out the binding specific parts of ->probe() and ->remove() to
enable the driver to support variants of the binding. This is useful in
order to keep backwards-compatibility while making it easy for a sub-
driver to deal only with the updated bindings rather than having to add
compatibility quirks all over the place.

Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-By: Joao Pinto <jpinto@synopsys.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>