net/mlx5: Enhance MCAM reg to allow query on access reg support

Enhance MCAM to allow the driver to query which access regs are
supported. For now, expose the regs needed for FW flashing.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>