Documentation: PCI: pci-endpoint: Fix EPF ops list

Documentation: PCI: pci-endpoint: Fix EPF ops list

With commit 5779dd0a7dbd7 ("PCI: endpoint: Use notification chain mechanism
to notify EPC events to EPF") the linkup callback has been removed and
replaced by EPC event notifications.

With commit 256ae475201b1 ("PCI: endpoint: Add pci_epf_ops to expose
function-specific attrs") a new (optional) add_cfs callback was added.
Update documentation accordingly.

Link: https://lore.kernel.org/linux-pci/20240418084924.1724703-1-alexander.stein@ew.tq-group.com
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>