configs: sandbox64: Enable BUTTON_ADC driver

Align the sandbox64 defconfig with sandbox defconfig. Enable missing
BUTTON ADC driver. This fixes ut_dm_dm_test_button_keys_adc test .

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>