net: ll_temac: Add ethtool support for coalesce parameters

Please note that the delays are calculated based on typical
parameters.  But as TEMAC is an HDL IP, designs may vary, and future
work might be needed to make this calculation configurable.

Signed-off-by: Esben Haabendal <esben@geanix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>