fs: Convert CONFIG_CMD_CBFS to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_CBFS

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: imply CMD_CBFS on SYS_COREBOOT]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 049fb27..8a16ed7 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -880,6 +880,15 @@
 endmenu
 
 menu "Filesystem commands"
+config CMD_CBFS
+	bool "Enable the 'cbfs' command"
+	help
+	  Define this to enable support for reading from a Coreboot
+	  filesystem. This is a ROM-based filesystem used for accessing files
+	  on systems that use coreboot as the first boot-loader and then load
+	  U-Boot to actually boot the Operating System. Available commands are
+	  cbfsinit, cbfsinfo, cbfsls and cbfsload.
+
 config CMD_EXT2
 	bool "ext2 command support"
 	help