pinctrl: rza1: Fix selector use for groups and functions

We must use a mutex around the generic_add functions and save the
function and group selector in case we need to remove them. Otherwise
the selector use will be racy for deferred probe at least.

Fixes: 5a49b644 ("pinctrl: Renesas RZ/A1 pin and gpio controller")
Reported-by: H. Nikolaus Schaller <hns@goldelico.com>
Cc: Christ van Willegen <cvwillegen@gmail.com>
Cc: Haojian Zhuang <haojian.zhuang@linaro.org>
Cc: Paul Cercueil <paul@crapouillou.net>
Cc: Sean Wang <sean.wang@mediatek.com>
Acked-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Tested-By: H. Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>