net: stmmac: Report taprio offload status

Report taprio offload status. This includes per txq and global
counters of window_drops and tx_overruns.

Window_drops count include count of frames dropped because of
queueMaxSDU setting and HLBF error. Transmission overrun counter
inform the user application whether any packets are currently being
transmitted on a particular queue during a gate-close event.DWMAC IPs
takes care Transmission overrun won't happen hence this is always 0.

Signed-off-by: Rohan G Thomas <rohan.g.thomas@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>