pinctrl: dynamically alloc temp array when parsing dt pinconf options

Allocating the temorary array in pinconf_generic_parse_dt_config on stack
might cause problems later on, when the number of options grows over time.
Therefore also allocate this array dynamically to be on the safe side.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>