regulator: make sure the regulator is available prior to the consumers.

Some systems are likely to want this to be subsys_initcall() to
make sure the regulator is available prior to the consumers.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>