pinctrl: berlin: select the pinctrl driver according to the SoC used

This patch prepares to remove the pinctrl driver selection from the
mach-berlin Kconfig. To do so, bool is replaced by def_bool.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>