PCI: rcar-gen4: Add .ltssm_control() for other SoC support

Sequence for controlling the LTSSM state machine is going to change
for SoCs like r8a779f0. Move the LTSSM code to a new callback
ltssm_control() and populate it for each SoCs.

This also warrants the addition of new compatibles for r8a779g0 and
r8a779h0. But since they are already part of the DT binding, it won't
make any difference.

Link: https://lore.kernel.org/linux-pci/20240611125057.1232873-4-yoshihiro.shimoda.uh@renesas.com


Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>