PCI: dwc: designware: Provide page_size to pci_epc_mem

Use the newly introduced __pci_epc_mem_init() instead of pci_epc_mem_init()
to provide page_size to pci_epc_mem. This is in preparation for
adding EP support to K2G which has a restriction that the
address region should be either divided into 1MB/2MB/4MB or 8MB
sizes (Ref: 11.14.4.9.1 Outbound Address Translation in K2G TRM SPRUHY8F
January 2016 – Revised May 2017).

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>