regulator: Add new driver for ST's PWM controlled voltage regulators

On some STMicroelectronics hardware reside regulators consisting
partly of a PWM input connected to the feedback loop. As the PWM
duty-cycle is varied the output voltage adapts. This driver
allows us to vary the output voltage by adapting the PWM input
duty-cycle.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/drivers/regulator/Kconfig b/drivers/regulator/Kconfig
index 6a79328..a6b29cb 100644
--- a/drivers/regulator/Kconfig
+++ b/drivers/regulator/Kconfig
@@ -432,6 +432,12 @@
 	 via I2C bus. S5M8767A have 9 Bucks and 28 LDOs output and
 	 supports DVS mode with 8bits of output voltage control.
 
+config REGULATOR_ST_PWM
+	tristate "STMicroelectronics PWM voltage regulator"
+	depends on ARCH_STI
+	help
+	 This driver supports ST's PWM controlled voltage regulators.
+
 config REGULATOR_TI_ABB
 	tristate "TI Adaptive Body Bias on-chip LDO"
 	depends on ARCH_OMAP