regulator: Allow regulator nodes to contain their own init data

Currently it is expected that regulator init data will be defined as a
series of sub-nodes from the node that bound in the driver. Add support
for a node to both bind in a driver and contain init data for that
regulator.

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