ASoC: arizona: Only allow input volume updates when inputs are enabled

Since we are automatically managing the mutes we may as well also manage
the volume update bits, disabling volume updates while none of the inputs
are active. Since we are doing this we may as well allow the volumes to
ramp together so only enable volume updates once at the end of power up.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>