Convert CONFIG_VGA_AS_SINGLE_DEVICE to Kconfig

This converts the following to Kconfig:
   CONFIG_VGA_AS_SINGLE_DEVICE

Once we migrate to driver model for video, we should be able to drop this
option.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index 3999246..a842da6 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -493,6 +493,16 @@
 	  erase functions and limited graphics rendition control). Normal
 	  output from U-Boot will pass through this filter.
 
+config VGA_AS_SINGLE_DEVICE
+	bool "Set the video as an output-only device"
+	depends on CFB_CONSOLE
+	default y
+	help
+	  If enable the framebuffer device will be initialized as an
+	  output-only device. The Keyboard driver will not be set up. This
+	  may be used if you have no keyboard device, or more than one
+	  (USB Keyboard, AT Keyboard).
+
 config VIDEO_CT69000
 	bool "Enable Chips & Technologies 69000 video driver"
 	depends on VIDEO
diff --git a/drivers/video/cfb_console.c b/drivers/video/cfb_console.c
index ac7c402..3a8e20b 100644
--- a/drivers/video/cfb_console.c
+++ b/drivers/video/cfb_console.c
@@ -58,12 +58,6 @@
  *					info);
  *				that fills a info buffer at i=row.
  *				s.a: board/eltec/bab7xx.
- * CONFIG_VGA_AS_SINGLE_DEVICE - If set the framebuffer device will be
- *				initialized as an output only device.
- *				The Keyboard driver will not be
- *				set-up.  This may be used, if you have
- *				no or more than one Keyboard devices
- *				(USB Keyboard, AT Keyboard).
  *
  * CONFIG_VIDEO_SW_CURSOR:    - Draws a cursor after the last
  *				character. No blinking is provided.