pinctrl: berlin: introduce berlin_pinctrl_probe_regmap()

This is to prepare for the next berlin4ct support, where we won't use
simple-mfd any more.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>