pinctrl: sh-pfc: Collect Renesas related CONFIGs in one place

Renesas related pinctrl CONFIGs are located in many places, which is
confusing.
This patch collects them into the same place, grouped in a new "Renesas
pinctrl drivers" menu.
This patch also moves pinctrl-rz{a1,a2,n1}.c into the sh-pfc folder.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87k0xoy4r7.wl-kuninori.morimoto.gx@renesas.com


[geert: Update path in MAINTAINERS]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>