Convert CONFIG_SYS_STDIO_DEREGISTER to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_STDIO_DEREGISTER

This option should never be enabled in SPL, so use
CONFIG_IS_ENABLED(SYS_STDIO_DEREGISTER) when checking the option.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Re-sync]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/common/usb_kbd.c b/common/usb_kbd.c
index a9872a6..5f9a64a 100644
--- a/common/usb_kbd.c
+++ b/common/usb_kbd.c
@@ -570,7 +570,7 @@
 /* Deregister the keyboard. */
 int usb_kbd_deregister(int force)
 {
-#ifdef CONFIG_SYS_STDIO_DEREGISTER
+#if CONFIG_IS_ENABLED(SYS_STDIO_DEREGISTER)
 	struct stdio_dev *dev;
 	struct usb_device *usb_kbd_dev;
 	struct usb_kbd_pdata *data;