net/mlx5: Unify QoS element type checks across NIC and E-Switch

Refactor the QoS element type support check by introducing a new
function, mlx5_qos_element_type_supported(), which handles element type
validation for both NIC and E-Switch schedulers.

This change removes the redundant esw_qos_element_type_supported()
function and unifies the element type checks into a single
implementation.

Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>