PCI: rockchip: Add per-lane PHY support

We distinguish the legacy PHY from newer per-lane PHYs by adding legacy_phy
flag.  Note that the legacy PHY is still the first option to be searched in
order not to break the backward compatibility of DTB.

Tested-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
[bhelgaas: tidy rockchip_pcie_get_phys()]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>