mfd: arizona: Change fast_start pdata name to better reflect functionality

The bit in the register enables MICBIAS fast startup when clear not when
set. This patch changes the name of this pdata option to soft_start to
better match the functionality. We rename rather than invert the
handling to keep the same default functionality, which is fast start
active.

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