adc: Add driver for STM32 ADC

This patch adds support for STMicroelectronics STM32 ADC (analog to
digital converter). It's originally based on Linux kernel v4.18-rcs
drivers/iio/adc/stm32-adc*. It's composed of:
- core driver (UCLASS_SIMPLE_BUS) manages common resources (clk, regu).
- child drivers (UCLASS_ADC) declare each ADC, channels and handle
  conversions.
This driver currently supports STM32H7 and STM32MP1 ADC.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/adc/stm32-adc-core.h b/drivers/adc/stm32-adc-core.h
new file mode 100644
index 0000000..ba0e10e
--- /dev/null
+++ b/drivers/adc/stm32-adc-core.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2018, STMicroelectronics - All Rights Reserved
+ * Author: Fabrice Gasnier <fabrice.gasnier@st.com>.
+ *
+ * Originally based on the Linux kernel v4.18 drivers/iio/adc/stm32-adc-core.h.
+ */
+
+#ifndef __STM32_ADC_H
+#define __STM32_ADC_H
+
+/*
+ * STM32 - ADC global register map
+ * ________________________________________________________
+ * | Offset |                 Register                    |
+ * --------------------------------------------------------
+ * | 0x000  |                Master ADC1                  |
+ * --------------------------------------------------------
+ * | 0x100  |                Slave ADC2                   |
+ * --------------------------------------------------------
+ * | 0x200  |                Slave ADC3                   |
+ * --------------------------------------------------------
+ * | 0x300  |         Master & Slave common regs          |
+ * --------------------------------------------------------
+ */
+#define STM32_ADC_MAX_ADCS		3
+#define STM32_ADCX_COMN_OFFSET		0x300
+
+#include <common.h>
+#include <clk.h>
+#include <dm.h>
+
+/**
+ * struct stm32_adc_common - stm32 ADC driver common data (for all instances)
+ * @base:		control registers base cpu addr
+ * @rate:		clock rate used for analog circuitry
+ * @aclk:		clock for the analog circuitry
+ * @bclk:		bus clock common for all ADCs
+ * @vref:		regulator reference
+ * @vref_uv:		reference supply voltage (uV)
+ */
+struct stm32_adc_common {
+	void __iomem *base;
+	unsigned long rate;
+	struct clk aclk;
+	struct clk bclk;
+	struct udevice *vref;
+	int vref_uv;
+};
+
+#endif