net/mlx5: Expose shared buffer registers bits and structs

Add the shared receive buffer management and configuration registers:
1. SBPR - Shared Buffer Pools Register
2. SBCM - Shared Buffer Class Management Register

Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>