configs: khadas-vim3(l): enable Function button support

Add options required to check the 'Function' button state.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/configs/khadas-vim3_defconfig b/configs/khadas-vim3_defconfig
index 5d16652..bc17430 100644
--- a/configs/khadas-vim3_defconfig
+++ b/configs/khadas-vim3_defconfig
@@ -31,6 +31,8 @@
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_ADC=y
 CONFIG_SARADC_MESON=y
+CONFIG_BUTTON=y
+CONFIG_BUTTON_ADC=y
 CONFIG_DM_I2C=y
 CONFIG_SYS_I2C_MESON=y
 CONFIG_DM_MMC=y