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/Kconfig b/common/Kconfig
index ff2b1a4..dbe5bb6 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -335,6 +335,15 @@
 	  Enable this option to supress this output. It can be obtained by
 	  calling stdio_print_current_devices() from board code.
 
+config SYS_STDIO_DEREGISTER
+	bool "Allow deregistering stdio devices"
+	default y if USB_KEYBOARD
+	help
+	  Generally there is no need to deregister stdio devices since they
+	  are never deactivated. But if a stdio device is used which can be
+	  removed (for example a USB keyboard) then this option can be
+	  enabled to ensure this is handled correctly.
+
 endmenu
 
 config SYS_NO_FLASH
diff --git a/common/stdio.c b/common/stdio.c
index ab9b05d..8e4a9be 100644
--- a/common/stdio.c
+++ b/common/stdio.c
@@ -37,7 +37,7 @@
 #define	CONFIG_SYS_DEVICE_NULLDEV	1
 #endif
 
-#ifdef	CONFIG_SYS_STDIO_DEREGISTER
+#if CONFIG_IS_ENABLED(SYS_STDIO_DEREGISTER)
 #define	CONFIG_SYS_DEVICE_NULLDEV	1
 #endif
 
@@ -245,7 +245,7 @@
 /* deregister the device "devname".
  * returns 0 if success, -1 if device is assigned and 1 if devname not found
  */
-#ifdef	CONFIG_SYS_STDIO_DEREGISTER
+#if CONFIG_IS_ENABLED(SYS_STDIO_DEREGISTER)
 int stdio_deregister_dev(struct stdio_dev *dev, int force)
 {
 	int l;
@@ -292,7 +292,7 @@
 
 	return stdio_deregister_dev(dev, force);
 }
-#endif	/* CONFIG_SYS_STDIO_DEREGISTER */
+#endif /* CONFIG_IS_ENABLED(SYS_STDIO_DEREGISTER) */
 
 int stdio_init_tables(void)
 {
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;