regulator: Add generic DT parsing for regulators

Looking up init data for regulators found on chips is a common operation
that can be handled in a generic way. The new helper function introduced
by this patch looks up the children of a given node by names specified
in a match table and fills that match table with information parsed from
the DT.

This is based on work by Rhyland Klein <rklein@nvidia.com>.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>