fm10k: add helper functions to set strings and data for ethtool stats

fm10k: add helper functions to set strings and data for ethtool stats

Reduce duplicate code and the amount of indentation by adding
fm10k_add_stat_strings and fm10k_add_ethtool_stats functions which help
add fm10k_stat structures to the ethtool stats callbacks. This helps
increase ease of use for future stat additions, and increases code
readability. Skip handling of the per-queue stats as these will be
reworked in a following patch.

Signed-off-by: Jacob Keller <[email protected]>
Tested-by: Krishneil Singh <[email protected]>
Signed-off-by: Jeff Kirsher <[email protected]>