regulator: introduce min_dropout_uV

Many voltage Regulators need a input voltage that is higher than the
output voltage. Allow to specify a minimum dropout voltage which will
be used later to find the best input voltage for regulators.

[Changed uv to uV for consistency and legibility -- broonie]
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/linux/regulator/driver.h

@@ -245,6 +245,7 @@ enum regulator_type {
  * @linear_min_sel: Minimal selector for starting linear mapping
  * @fixed_uV: Fixed voltage of rails.
  * @ramp_delay: Time to settle down after voltage change (unit: uV/us)
+ * @min_dropout_uV: The minimum dropout voltage this regulator can handle
  * @linear_ranges: A constant table of possible voltage ranges.
  * @n_linear_ranges: Number of entries in the @linear_ranges table.
  * @volt_table: Voltage mapping table (if table based mapping)
@@ -292,6 +293,7 @@ struct regulator_desc {
 	unsigned int linear_min_sel;
 	int fixed_uV;
 	unsigned int ramp_delay;
+	int min_dropout_uV;
 
 	const struct regulator_linear_range *linear_ranges;
 	int n_linear_ranges;