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>