dm: adc: Add driver for Rockchip SARADC

The ADC can support some channels signal-ended some bits Successive Approximation
Register (SAR) A/D Converter, like 6-channel and 10-bit. It converts the analog
input signal into some bits binary digital codes.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/drivers/adc/Makefile b/drivers/adc/Makefile
index cebf26d..4b5aa69 100644
--- a/drivers/adc/Makefile
+++ b/drivers/adc/Makefile
@@ -8,3 +8,4 @@
 obj-$(CONFIG_ADC) += adc-uclass.o
 obj-$(CONFIG_ADC_EXYNOS) += exynos-adc.o
 obj-$(CONFIG_ADC_SANDBOX) += sandbox.o
+obj-$(CONFIG_SARADC_ROCKCHIP) += rockchip-saradc.o