net: stmmac: add per-queue TX & RX coalesce ethtool support

Extending the driver to support per-queue RX and TX coalesce settings in
order to support below commands:

To show per-queue coalesce setting:-
 $ ethtool --per-queue <DEVNAME> queue_mask <MASK> --show-coalesce

To set per-queue coalesce setting:-
 $ ethtool --per-queue <DEVNAME> queue_mask <MASK> --coalesce \
     [rx-usecs N] [rx-frames M] [tx-usecs P] [tx-frames Q]

Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>