net/mlx5: Expose MPEIN (Management PCIE INfo) register layout

Expose PRM layout for handling MPEIN (Management PCIE Info). It will be
used in the downstream patch for querying MPEIN via the driver.

Signed-off-by: Aya Levin <ayal@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>