net/mlx5e: Report RS-FEC histogram statistics via ethtool

net/mlx5e: Report RS-FEC histogram statistics via ethtool

Add support for reporting RS-FEC histogram counters by reading them
from the RS_FEC_HISTOGRAM_GROUP in the PPCNT register.

Co-developed-by: Yael Chemla <ychemla@nvidia.com>
Signed-off-by: Yael Chemla <ychemla@nvidia.com>
Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Yael Chemla <ychemla@nvidia.com>
Link: https://patch.msgid.link/20250924124037.1508846-5-vadim.fedorenko@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>