net/mlx5: allocate flow meter registers

net/mlx5: allocate flow meter registers

Meter need the metadata REG_C to have the color match between the prefix
flow and the meter flow.

As the user define or metadata feature will both use the REG_C in the
suffix flow, the color match register meter uses will not impact the
register use in the later sub flow.

Another case is that tag is add before meter flow. In this case, meter
should not touch the register the tag action is using. To avoid that
case, meter should reserve the REG_C's used by user defined MLX5_APP_TAG.

Signed-off-by: Suanming Mou <suanmingm@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>