driver: net: ethernet: cpsw: implement interrupt pacing via ethtool

This patch implements support for interrupt pacing block of CPSW via ethtool
Inetrrupt pacing block is common of both the ethernet interface in
dual emac mode

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>