PCI/TPH: Allow TPH enable for RCiEPs

PCI/TPH: Allow TPH enable for RCiEPs

Previously, pcie_enable_tph() only enabled TLP Processing Hints (TPH) if
both the Endpoint and its Root Port advertised TPH support.

Root Complex Integrated Endpoints (RCiEPs) are directly integrated into a
Root Complex and do not have an associated Root Port, so pcie_enable_tph()
never enabled TPH for RCiEPs.

PCIe r7.0 doesn't seem to include a way to learn whether a Root Complex
supports TPH, but sec 2.2.7.1.1 says Functions that lack TPH support should
ignore TPH, and maybe the same is true for Root Complexes:

  A Function that does not support the TPH Completer or Routing capability
  and receives a transaction with the TH bit [which indicates the presence
  of TPH in the TLP header] Set is required to ignore the TH bit and handle
  the Request in the same way as Requests of the same transaction type
  without the TH bit Set.

Allow drivers to enable TPH for any RCiEP with a TPH Requester Capability.

Fixes: f69767a1ada3 ("PCI: Add TLP Processing Hints (TPH) support")
Signed-off-by: George Abraham P <george.abraham.p@intel.com>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260109052923.1170070-1-george.abraham.p@intel.com