net/mlx5: E-switch, Allow setting share/max tx rate limits of rate groups

Provide eswitch API to allow controlling group rate limits. Use it to
implement devlink_ops->mlx5_devlink_rate_node_tx_{share|max}_set().

The share rate will create relative bandwidth share on the groups level
while within the group the user can set shared rate on the member vports
of that group and this rate will be relative to the group's share rate.
The group with the highest shared rate will get a BW share of 100 and
the rest of the groups will get a value that reflects the ratio between
their share rate and the maximum share rate.

Example:
Created four rate groups with tx_share limits:

$ devlink port function rate add \
    pci/0000:06:00.0/group_1 tx_share 30gbit
$ devlink port function rate add \
    pci/0000:06:00.0/group_2 tx_share 20gbit
$ devlink port function rate add \
    pci/0000:06:00.0/group_3 tx_share 20gbit
$ devlink port function rate add \
    pci/0000:06:00.0/group_4 tx_share 10gbit

Assuming link speed is 50 Gbit/sec ratio divider will be
50 / (30+20+20+10) = 0.625. Normalized rate values for the groups:

<group_1> 30 * 0.625 = 18.75 Gbit/sec
<group_2> 20 * 0.625 = 12.5 Gbit/sec
<group_3> 20 * 0.625 = 12.5 Gbit/sec
<group_4> 10 * 0.625 = 6.25 Gbit/sec

Rate group with unlimited tx_share rate will receive minimum BW value
(1Mbit/sec) if presented any group with tx_share rate limit. This allow
to not drop all packets in case of heavy traffic.

Co-developed-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Dmytro Linkin <dlinkin@nvidia.com>
Reviewed-by: Huy Nguyen <huyn@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>