Enable PCIe Host controller channel 0 on R-Car S4-8 Spider board.

Since this board has an Oculink connector, CLKREQ# pin of PFC for PCIe
should not be used. So, using a GPIO is used to output the clock instead.
Otherwise the controller cannot detect a PCIe device.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230905012404.2915246-3-yoshihiro.shimoda.uh@renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>