PCI: rzg3s-host: Use pci_generic_config_write() for the root bus

PCI: rzg3s-host: Use pci_generic_config_write() for the root bus

The Renesas RZ/G3S host controller allows writing to read-only PCIe
configuration registers when the RZG3S_PCI_PERM_CFG_HWINIT_EN bit is set in
the RZG3S_PCI_PERM register. However, callers of struct pci_ops::write
expect the semantics defined by the PCIe specification, meaning that writes
to read-only registers must not be allowed.

The previous custom struct pci_ops::write implementation for the root bus
temporarily enabled write access before calling pci_generic_config_write().
This breaks the expected semantics.

Remove the custom implementation and simply use pci_generic_config_write().

Along with this change, the updates of the PCI_PRIMARY_BUS,
PCI_SECONDARY_BUS, and PCI_SUBORDINATE_BUS registers were moved so that
they no longer depends on the RZG3S_PCI_PERM_CFG_HWINIT_EN bit in the
RZG3S_PCI_PERM_CFG register, since these registers are R/W.

Fixes: 7ef502fb35b2 ("PCI: Add Renesas RZ/G3S host controller driver")
Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://patch.msgid.link/20251217111510.138848-2-claudiu.beznea.uj@bp.renesas.com