mfd: arizona: Add device tree binding to specify mono outputs

Add device tree bindings to support specifying outputs from the chip as
mono outputs. Whilst we are doing it change the out_mono pdata from a
bool to an int, because Sparse gets upset about using ARRAY_SIZE on
bools.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>