net/mlx5: Support new MR features

This patch adds the following items to IFC file.

1. MLX5_MKC_ACCESS_MODE_KSM enum value for creating KSM memory keys.
KSM access mode used when indirect MKey associated with fixed memory
size entries.

2. null_mkey field that is used to indicate non-present KLM/KSM
entries, where it causes the device to generate page fault event
when trying to access it.

3. struct mlx5_ifc_cmd_hca_cap_bits capability bits indicating
related value/field is supported:
* fixed_buffer_size - MLX5_MKC_ACCESS_MODE_KSM
* umr_extended_translation_offset - translation_offset_42_16
    in UMR ctrl segment
* null_mkey - null_mkey in QUERY_SPECIAL_CONTEXTS

Signed-off-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>