MFC r347275:
Enhance MCAM reg to allow query on access reg support in mlx5core.

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

Linux commit:
0ab87743cc8c5bcd482daf71961ed5fc45349e01

Submitted by: slavash@
Sponsored by: Mellanox Technologies