PCI: fu740: Add SiFive FU740 PCIe host controller driver

Add driver for the SiFive FU740 PCIe host controller.
This controller is based on the DesignWare PCIe core.

Co-developed-by: Henry Styles <hes@sifive.com>
Co-developed-by: Erik Danie <erik.danie@sifive.com>
Co-developed-by: Greentime Hu <greentime.hu@sifive.com>
Link: https://lore.kernel.org/r/20210504105940.100004-6-greentime.hu@sifive.com


Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Henry Styles <hes@sifive.com>
Signed-off-by: Erik Danie <erik.danie@sifive.com>
Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>