ARM: dts: Add #pinctrl-cells for pinctrl-single instances

Drivers using pinctrl-single,pins have #pinctrl-cells = <1>, while
pinctrl-single,bits need #pinctrl-cells = <2>.

Note that this patch can be optionally applied separately from the
driver changes as the driver supports also the legacy binding without
#pinctrl-cells.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>