regulator: Enable max8925 i2c sequence for control

Force to enable i2c as power up/down sequence. Otherwise, SD/LDO can't
be enabled or disabled via accessing i2c bus.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Cc: Liam Girdwood <lrg@slimlogic.co.uk>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>