regulator: Add soft start support

Some regulators support a "soft start" feature where the voltage
ramps up slowly when the regulator is enabled. Add an op
(set_soft_start) and a DT property + constraint to support this.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/include/linux/regulator/machine.h b/include/linux/regulator/machine.h
index 8ffb061..7f7d0a3 100644
--- a/include/linux/regulator/machine.h
+++ b/include/linux/regulator/machine.h
@@ -142,6 +142,7 @@
 	unsigned boot_on:1;	/* bootloader/firmware enabled regulator */
 	unsigned apply_uV:1;	/* apply uV constraint if min == max */
 	unsigned ramp_disable:1; /* disable ramp delay */
+	unsigned soft_start:1;	/* ramp voltage slowly */
 	unsigned pull_down:1;	/* pull down resistor when regulator off */
 };