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/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 2dbeacc..8d51c49 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -167,6 +167,7 @@
 CONFIG_CONSOLE_TRUETYPE=y
 CONFIG_CONSOLE_TRUETYPE_CANTORAONE=y
 CONFIG_VIDEO_SANDBOX_SDL=y
+CONFIG_FS_CBFS=y
 CONFIG_CMD_DHRYSTONE=y
 CONFIG_TPM=y
 CONFIG_LZ4=y