net/mlx5e: Add capability check for vnic counters

Add missing capability check for each of the vnic counters exposed by
devlink health reporter, and thus avoid unexpected behavior due to
invalid access to registers.

While at it, read only the exact number of bits for each counter whether
it was 32 bits or 64 bits.

Fixes: b0bc615d ("net/mlx5: Add vnic devlink health reporter to PFs/VFs")
Fixes: a33682e4 ("net/mlx5e: Expose catastrophic steering error counters")
Signed-off-by: Lama Kayal <lkayal@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Maher Sanalla <msanalla@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>