fwctl/mlx5: Support for communicating with mlx5 fw

mlx5 FW has a built in security context called UID. Each UID has a set of
permissions controlled by the kernel when it is created and every command
is tagged by the kernel with a particular UID. In general commands cannot
reach objects outside of their UID and commands cannot exceed their UID's
permissions. These restrictions are enforced by FW.

This mechanism has long been used in RDMA for the devx interface where
RDMA will sent commands directly to the FW and the UID limitations
restrict those commands to a ib_device/verbs security domain. For instance
commands that would effect other VFs, or global device resources. The
model is suitable for unprivileged userspace to operate the RDMA
functionality.

The UID has been extended with a "tools resources" permission which allows
additional commands and sub-commands that are intended to match with the
scope limitations set in FWCTL. This is an alternative design to the
"command intent log" where the FW does the enforcement rather than having
the FW report the enforcement the kernel should do.

Consistent with the fwctl definitions the "tools resources" security
context is limited to the FWCTL_RPC_CONFIGURATION,
FWCTL_RPC_DEBUG_READ_ONLY, FWCTL_RPC_DEBUG_WRITE, and
FWCTL_RPC_DEBUG_WRITE_FULL security scopes.

Like RDMA devx, each opened fwctl file descriptor will get a unique UID
associated with each file descriptor.

The fwctl driver is kept simple and we reject commands that can create
objects as the UID mechanism relies on the kernel to track and destroy
objects prior to detroying the UID. Filtering into fwctl sub scopes is
done inside the driver with a switch statement. This substantially limits
what is possible to primarily query functions ad a few limited set
operations.

mlx5 already has a robust infrastructure for delivering RPC messages to
fw. Trivially connect fwctl's RPC mechanism to mlx5_cmd_do(). Enforce the
User Context ID in every RPC header accepted from the FD so the FW knows
the security context of the issuing ID.

Link: https://patch.msgid.link/r/7-v5-642aa0c94070+4447f-fwctl_jgg@nvidia.com
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

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