doc: fix description of some mlx5 features

doc: fix description of some mlx5 features

The support of the new RTE_FLOW_ITEM_TYPE_INTEGRITY
was added in the release notes 21.02 by mistake.

The support of the Sub-Function representors was missing
in the release notes and the mlx5 guide.

Fixes: 79f8952783d0 ("net/mlx5: support integrity flow item")
Fixes: cb95feefdd03 ("net/mlx5: support sub-function representor")
Signed-off-by: Asaf Penso <asafp@nvidia.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>