documentation: Extend pinctrl docs for Meson8b

Add the compatible string for Meson8b in Meson pinctrl documentation
and add new information for Meson8b in source code comments.

Signed-off-by: Carlo Caione <carlo@endlessm.com>
Acked-by: Beniamino Galvani <b.galvani@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
2 files changed