adc: add missing depends on ADC for controller drivers

The ADC controller drivers are obviously all depending on ADC symbol
being selected.

While they don't seem to fail to build without, they won't be useful
without that symbol selected, so let's make sure the options aren't
shown in menuconfig when ADC isn't selected.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
diff --git a/drivers/adc/Kconfig b/drivers/adc/Kconfig
index a01d738..c9cdbe6 100644
--- a/drivers/adc/Kconfig
+++ b/drivers/adc/Kconfig
@@ -13,6 +13,7 @@
 
 config ADC_EXYNOS
 	bool "Enable Exynos 54xx ADC driver"
+	depends on ADC
 	help
 	  This enables basic driver for Exynos ADC compatible with Exynos54xx.
 	  It provides:
@@ -22,6 +23,7 @@
 
 config ADC_SANDBOX
 	bool "Enable Sandbox ADC test driver"
+	depends on ADC
 	help
 	  This enables driver for Sandbox ADC device emulation.
 	  It provides:
@@ -31,6 +33,7 @@
 
 config SARADC_MESON
 	bool "Enable Amlogic Meson SARADC driver"
+	depends on ADC
 	imply REGMAP
 	help
 	  This enables driver for Amlogic Meson SARADC.
@@ -41,6 +44,7 @@
 
 config SARADC_ROCKCHIP
 	bool "Enable Rockchip SARADC driver"
+	depends on ADC
 	help
 	  This enables driver for Rockchip SARADC.
 	  It provides: