adc: add Amlogic Meson SAR ADC driver

This patch adds the driver for the Amlogic Meson Successive Approximation
Register (SAR) A/D Converter based on the Linux IIO driver thanks to the
great work of Martin Blumenstingl.
The driver has been adapted to U-Boot and the ADC UClass.

This patch depends on the regmap "regmap: add regmap_update_bits() helper"
patch and has been tested using the newly introducted "adc" CLI command
in the "cmd: add ADC cli commands" patch.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/drivers/adc/Kconfig b/drivers/adc/Kconfig
index 8094420..93e27f1 100644
--- a/drivers/adc/Kconfig
+++ b/drivers/adc/Kconfig
@@ -29,6 +29,16 @@
 	  - 16-bit resolution
 	  - single and multi-channel conversion mode
 
+config SARADC_MESON
+	bool "Enable Amlogic Meson SARADC driver"
+	imply REGMAP
+	help
+	  This enables driver for Amlogic Meson SARADC.
+	  It provides:
+	  - 8 analog input channels
+	  - 1O or 12 bits resolution
+	  - Up to 1MSPS of sample rate
+
 config SARADC_ROCKCHIP
 	bool "Enable Rockchip SARADC driver"
 	help