pinctrl: berlin: drop SoC stub provided regmap

With convertsion to simple-mfd sub-nodes, drop the regmap registration
by SoC stubs.

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