mfd: tps65910: Initialize mfd devices after all initialization done

Add sub devices of tps65910 after all initialization like interrupt,
clock etc. is done. This will make sure that require data gets
initialized properly before sub devices probe's get called.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>