dm: adc: Add SPL_ADC Kconfig symbol for use of ADC in SPL

What model of Radxa ZERO 3W/3E board can be identified using ADC at
runtime, add a Kconfig symbol to allow use of ADC in SPL.

This will be used to identify board model in SPL to allow loading
correct FIT configuration and FDT for U-Boot proper at SPL phase.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/drivers/adc/Kconfig b/drivers/adc/Kconfig
index c9cdbe6..37235f5 100644
--- a/drivers/adc/Kconfig
+++ b/drivers/adc/Kconfig
@@ -1,5 +1,6 @@
 config ADC
 	bool "Enable ADC drivers using Driver Model"
+	depends on DM
 	help
 	  This enables ADC API for drivers, which allows driving ADC features
 	  by single and multi-channel methods for:
@@ -11,6 +12,10 @@
 	  - support supply's phandle with auto-enable
 	  - supply polarity setting in fdt
 
+config SPL_ADC
+	bool "Enable ADC drivers using Driver Model in SPL"
+	depends on SPL_DM
+
 config ADC_EXYNOS
 	bool "Enable Exynos 54xx ADC driver"
 	depends on ADC