regulator: Make bulk API support optional supplies

Make it possible to use the bulk API with optional supplies, by allowing
the consumer to marking supplies as optional in the regulator_bulk_data.

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/linux/regulator/consumer.h

@@ -140,6 +140,8 @@ struct regulator;
  *
  * @supply:   The name of the supply.  Initialised by the user before
  *            using the bulk regulator APIs.
+ * @optional: The supply should be considered optional. Initialised by the user
+ *            before using the bulk regulator APIs.
  * @consumer: The regulator consumer for the supply.  This will be managed
  *            by the bulk API.
  *
@@ -149,6 +151,7 @@ struct regulator;
  */
 struct regulator_bulk_data {
 	const char *supply;
+	bool optional;
 	struct regulator *consumer;
 
 	/* private: Internal use */