PCI: endpoint: Pass page size as argument to pci_epc_mem_init()

pci_epc_mem_init() internally used page size equal to *PAGE_SIZE* to
manage the address space so instead just pass the page size as a
argument to pci_epc_mem_init().

Also make pci_epc_mem_init() as a C function instead of a macro function
in preparation for adding support for pci-epc-mem core to handle multiple
windows.

Link: https://lore.kernel.org/r/1588854799-13710-5-git-send-email-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>