intel: Update drivers to use ethtool_sprintf

Update the Intel drivers to make use of ethtool_sprintf. The general idea
is to reduce code size and overhead by replacing the repeated pattern of
string printf statements and ETH_STRING_LEN counter increments.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Acked-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>