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>
3 files changed