ASoC: arizona: Update handling for input change on an active FLL

Currently, the driver places no restrictions on changes that can be
applied to an active FLL. However, it is only possible to change the
input for an active FLL, to change the output the FLL should be stopped
and then recofigured. This patch disallows changes in output frequency
and adds some additional handling to ensure the output remains
consistent across an input transition.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>