PCI: uniphier-ep: Add SoC data structure

PCI: uniphier-ep: Add SoC data structure

Define SoC data structure that includes pci_epc_features, SoC-dependent
callback functions and flags to distinguish the behavior of each SoC.
The callback functions define init() to initialize the controller and
wait() to wait until initialization is completed.

Rename uniphier_pcie_init_ep() to uniphier_pcie_pro5_init_ep() for
initializing PCIe controller implemented in Pro5 SoC. And Pro5 SoC
doesn't have wait() function.

Link: https://lore.kernel.org/r/1644480596-20037-3-git-send-email-hayashi.kunihiko@socionext.com
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>