PCI: Add Renesas RZ/G3S host controller driver

PCI: Add Renesas RZ/G3S host controller driver

The Renesas RZ/G3S features a PCIe IP that complies with the PCI Express
Base Specification 4.0 and supports speeds of up to 5 GT/s. It functions
only as a root complex, with a single-lane (x1) configuration. The
controller includes Type 1 configuration registers, as well as IP
specific registers (called AXI registers) required for various adjustments.

Hardware manual can be downloaded from the address in the "Link" section.
The following steps should be followed to access the manual:
1/ Click the "User Manual" button
2/ Click "Confirm"; this will start downloading an archive
3/ Open the downloaded archive
4/ Navigate to r01uh1014ej*-rzg3s-users-manual-hardware -> Deliverables
5/ Open the file r01uh1014ej*-rzg3s.pdf

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://www.renesas.com/en/products/rz-g3s?queryID=695cc067c2d89e3f271d43656ede4d12
Link: https://patch.msgid.link/20251119143523.977085-3-claudiu.beznea.uj@bp.renesas.com