generic: add missing symbol

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46462 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/generic/config-4.1

@@ -1092,6 +1092,7 @@ CONFIG_FAT_DEFAULT_IOCHARSET="iso8859-1"
 # CONFIG_FB_SYS_FILLRECT is not set
 # CONFIG_FB_SYS_FOPS is not set
 # CONFIG_FB_SYS_IMAGEBLIT is not set
+# CONFIG_FB_TFT is not set
 # CONFIG_FB_TILEBLITTING is not set
 # CONFIG_FB_TMIO is not set
 # CONFIG_FB_TRIDENT is not set