PCI: rzg3s-host: Add support for RZ/V2H(P) SoC

Add support for the RZ/V2H(P) SoC PCIe controllers to the rzg3s-host
driver.

The RZ/V2H(P) SoC features two independent PCIe controllers that share
four physical lanes. The hardware supports two configuration modes:
single x4 mode where the first controller uses all four lanes, or dual
x2 mode where both controllers use two lanes each.

Introduce a setup_lanes() function pointer to configure the PCIe lanes
based on the hardware instance. Implement rzv2h_pcie_setup_lanes() to
detect the configuration at boot time and program the lane mode via the
system controller.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Tested-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Link: https://patch.msgid.link/20260629220932.861445-5-prabhakar.mahadev-lad.rj@bp.renesas.com