This patch adds the MMC management counters support.
MMC module is an extension of the register address
space and all the hardware counters can be accessed
via ethtoo -S ethX.

Note that, the MMC interrupts remain masked and the logic
to handle this kind of interrupt will be added later (if
actually useful).
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>