stmmac: perform hw bus configuration

On some platforms it can be required a different
configuration of the bus. This can be done
by invoking the bus_setup. It is defined
for all the platforms that needs this kind of
configuration.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>