net/mlx5: Add support for device steering tag

net/mlx5: Add support for device steering tag

Background, from PCIe specification 6.2.

TLP Processing Hints (TPH)
--------------------------
TLP Processing Hints is an optional feature that provides hints in
Request TLP headers to facilitate optimized processing of Requests that
target Memory Space. These Processing Hints enable the system hardware
(e.g., the Root Complex and/or Endpoints) to optimize platform
resources such as system and memory interconnect on a per TLP basis.
Steering Tags are system-specific values used to identify a processing
resource that a Requester explicitly targets. System software discovers
and identifies TPH capabilities to determine the Steering Tag allocation
for each Function that supports TPH.

This patch adds steering tag support for mlx5 based NICs by:

- Enabling the TPH functionality over PCI if both FW and OS support it.
- Managing steering tags and their matching steering indexes by
  writing a ST to an ST index over the PCI configuration space.
- Exposing APIs to upper layers (e.g.,mlx5_ib) to allow usage of
  the PCI TPH infrastructure.

Further details:
- Upon probing of a device, the feature will be enabled based
  on both capability detection and OS support.

- It will retrieve the appropriate ST for a given CPU ID and memory
  type using the pcie_tph_get_cpu_st() API.

- It will track available ST indices according to the configuration
  space table size (expected to be 63 entries), reserving index 0 to
  indicate non-TPH use.

- It will assign a free ST index with a ST using the
  pcie_tph_set_st_entry() API.

- It will reuse the same index for identical (CPU ID + memory type)
  combinations by maintaining a reference count per entry.

- It will expose APIs to upper layers (e.g., mlx5_ib) to allow usage of
  the PCI TPH infrastructure.

- SF will use its parent PF stuff.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://patch.msgid.link/de1ae7398e9e34eacd8c10845683df44fc9e32f8.1752752567.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>