add Kconfig for fsuuid command

CONFIG_CMD_FS_UUID was neither whitelisted, nor was it declared in
Kconfig.
Now it can be enabled in .config and defconfig as expected.

Signed-off-by: Josua Mayer <josua.mayer97@gmail.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 13dc46a..5088823 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -831,6 +831,11 @@
 	  Enables filesystem commands (e.g. load, ls) that work for multiple
 	  fs types.
 
+config CMD_FS_UUID
+	bool "fsuuid command"
+	help
+	  Enables fsuuid command for filesystem UUID.
+
 config CMD_MTDPARTS
 	depends on ARCH_SUNXI
 	bool "MTD partition support"