PCI: rockchip-dwc: Add Rockchip RK356X host controller driver

PCI: rockchip-dwc: Add Rockchip RK356X host controller driver

Add a driver for the DesignWare-based PCIe controller found on
RK356X. The existing pcie-rockchip-host driver is only used for
the Rockchip-designed IP found on RK3399.

Link: https://lore.kernel.org/r/20210625065511.1096935-1-xxm@rock-chips.com
Tested-by: Peter Geis <pgwipeout@gmail.com>
Signed-off-by: Simon Xue <xxm@rock-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Rob Herring <robh@kernel.org>