PCI: endpoint: Add the function number as argument to EPC ops

This patch updates the prototype of most handlers from 'struct
pci_epc_ops' so the EPC library can now support multi-function devices.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@free-electrons.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>