net/mlx5e: Dynamically allocate TIRs in RSS contexts

Move from static to dynamic memory allocations for TIR.
This is in preparation to supporting on-demand TIR operations in
downstream patches, where every RSS context will be init with an
empty set of TIRs.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>