power: regulator: Add support for stm32-vrefbuf

Add regulator driver for STM32 voltage reference buffer which can be
used as voltage reference for ADCs, DACs and external components through
dedicated VREF+ pin.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/power/regulator/Makefile b/drivers/power/regulator/Makefile
index d73a6e3..16208af 100644
--- a/drivers/power/regulator/Makefile
+++ b/drivers/power/regulator/Makefile
@@ -22,5 +22,6 @@
 obj-$(CONFIG_$(SPL_)DM_REGULATOR_PBIAS) += pbias_regulator.o
 obj-$(CONFIG_$(SPL_)DM_REGULATOR_LP873X) += lp873x_regulator.o
 obj-$(CONFIG_$(SPL_)DM_REGULATOR_LP87565) += lp87565_regulator.o
+obj-$(CONFIG_$(SPL_)DM_REGULATOR_STM32_VREFBUF) += stm32-vrefbuf.o
 obj-$(CONFIG_DM_REGULATOR_TPS65910) += tps65910_regulator.o
 obj-$(CONFIG_$(SPL_)DM_REGULATOR_STPMU1) += stpmu1.o