PCI: kirin: Reorganize the PHY logic inside the driver

The pcie-kirin PCIe driver contains internally a PHY interface for
Kirin 960.

As the next patches will add support for using an external PHY driver,
reorganize the driver in a way that the PHY part will be self-contained.

This could be moved to a separate PHY driver, but a change like that would
mean a non-backward-compatible DT schema change.

Link: https://lore.kernel.org/r/ad2f4aa6bbb71d5c9af0139704672f75f12644fc.1634812676.git.mchehab+huawei@kernel.orgSigned-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Xiaowei Song <songxiaowei@hisilicon.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>