net: stmmac: xgmac: Disable MMC interrupts by default

MMC interrupts were being enabled, which is not what we want because it
will lead to a storm of interrupts that are not handled at all. Fix it
by disabling all MMC interrupts for XGMAC.

Fixes: b6cdf09f ("net: stmmac: xgmac: Implement MMC counters")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>