net/mlx5: Add structure layout and defines for MFRL register

Add needed structure layouts and defines for MFRL (Management Firmware
Reset Level) register. This structure will be used for the firmware
upgrade and reset flow in the downstream patches.

Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>