net/mlx5: E-switch, Enable devlink port tx_{share|max} rate control

Register devlink rate leaf object for every eswitch vport.
Implement devlink ops that enable setting shared and max tx rates
through devlink API.
Extract common eswitch code from existing tx rate set function that is
accessed through NDO to be reused for the devlink. Values configured
with NDO API are not visible for the devlink API, therefore shouldn't be
used simultaneously.

When normalizing the BW share value, dividing the desired minimum rate
by the common divider results in losing information since the quotient
is rounded down. This has a significant affect on configurations of low
rate where the round down eliminates a large percentage of the total
rate. To improve the formula, round up the division result to make sure
that the BW share is at least the value it was supposed to be and won't
lost a significant amount of the expected value.

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>