fs: Kconfig: Add a separate config for FS_CBFS

Rather than using CMD_CBFS for both the filesystem and its command, we
should have a separate option for each. This allows us to enable CBFS
support without the command, if desired, which reduces U-Boot's size
slightly.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: imply FS_CBFS on SYS_COREBOOT]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/fs/Makefile b/fs/Makefile
index 51d06fc..5c90656 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -12,7 +12,7 @@
 else
 obj-y				+= fs.o
 
-obj-$(CONFIG_CMD_CBFS) += cbfs/
+obj-$(CONFIG_FS_CBFS) += cbfs/
 obj-$(CONFIG_CMD_CRAMFS) += cramfs/
 obj-$(CONFIG_FS_EXT4) += ext4/
 obj-y += fat/