By default, all gmac cores disable the PCS block and always
enable the PMT.

Note that this is done in a different way by 3.x and 4.x cores.

With this rework, PCS and PMT interrupt masks can be driven by
parameters now moved inside the mac_device_info structure
and the settings follow what the HW capability register reports.
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>