input: button_kbd: make driver complementary to gpio buttons

Remove need of dts binding for button keyboard since it reuses
gpio-keys binding. Select gpio-keys driver if button keyboard
is selected since button keyboard can not operate on its own.

Tested-by: Svyatoslav Ryhel <clamor95@gmail.com> # HTC One X T30
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/input/Kconfig b/drivers/input/Kconfig
index 32360d9..c2b365a 100644
--- a/drivers/input/Kconfig
+++ b/drivers/input/Kconfig
@@ -48,8 +48,8 @@
 
 config BUTTON_KEYBOARD
 	bool "Buttons as keyboard"
-	depends on BUTTON_GPIO
 	depends on DM_KEYBOARD
+	select BUTTON_GPIO
 	help
 	  Enable support for mapping buttons to keycode events. Use linux,code button driver
 	  dt node to define button-event mapping.