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/configs/theadorable_defconfig b/configs/theadorable_defconfig
index 52c49d0..24a0dbe 100644
--- a/configs/theadorable_defconfig
+++ b/configs/theadorable_defconfig
@@ -42,5 +42,6 @@
 CONFIG_DEBUG_UART_SHIFT=2
 CONFIG_SYS_NS16550=y
 CONFIG_VIDEO_MVEBU=y
+CONFIG_CFB_CONSOLE=y
 CONFIG_REGEX=y
 CONFIG_LIB_RAND=y