sandbox64: enable button

Enable the support of button (driver and command) on sandbox64.
Reviewed-by: NSimon Glass <sjg@chromium.org>
Signed-off-by: NPhilippe Reynes <philippe.reynes@softathome.com>

configs/sandbox64_defconfig

@@ -93,6 +93,8 @@ CONFIG_ADC=y
 CONFIG_ADC_SANDBOX=y
 CONFIG_AXI=y
 CONFIG_AXI_SANDBOX=y
+CONFIG_BUTTON=y
+CONFIG_BUTTON_GPIO=y
 CONFIG_CLK=y
 CONFIG_CPU=y
 CONFIG_DM_DEMO=y