pinctrl: make pinconf.h self-contained

This header uses 'bool', but it does not include any header by itself.

So, it could cause unknown type name error, depending on the header
include order, although probably <linux/types.h> has been included by
someone else.

Include <linux/types.h> to make it self-contained.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>