sandbox: add ADC unit tests

This commit adds unit tests for ADC uclass's methods using sandbox ADC.

Testing proper ADC binding:
- dm_test_adc_bind()                    - device binding
- dm_test_adc_wrong_channel_selection() - checking wrong channel selection

Testing ADC supply operations:
- dm_test_adc_supply():
  - Vdd/Vss values validating
  - Vdd regulator updated value validating
  - Vdd regulator's auto enable state validating

Testing ADC operations results:
- dm_test_adc_single_channel_conversion() - single channel start/data
- dm_test_adc_single_channel_shot()       - single channel shot
- dm_test_adc_multi_channel_conversion()  - multi channel start/data
- dm_test_adc_multi_channel_shot()        - multi channel single shot

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

include/power/sandbox_pmic.h

@@ -126,6 +126,10 @@ enum {
 #define SANDBOX_BUCK1_AUTOSET_EXPECTED_UA	200000
 #define SANDBOX_BUCK1_AUTOSET_EXPECTED_ENABLE	true
 
+/* BUCK2: for testing sandbox ADC's supply */
+#define SANDBOX_BUCK2_INITIAL_EXPECTED_UV	3000000
+#define SANDBOX_BUCK2_SET_UV			3300000
+
 /* LDO1/2 for testing regulator_list_autoset() */
 #define SANDBOX_LDO1_AUTOSET_EXPECTED_UV	1800000
 #define SANDBOX_LDO1_AUTOSET_EXPECTED_UA	100000