cmd: fdt: Use separate CMD_FDT Kconfig entry instead of OF_LIBFDT

Create CMD_FDT Kconfig entry to have an option to disable fdt command
which is not required for small configuration which requires libfdt
only.
Enable it by default for all targets which enables OF_LIBFDT.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
[trini: Fixup flea3/sandbox/id8313/siemens-am33xx/smartweb]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index fe8b4f0..8703cdb 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -173,6 +173,13 @@
 	help
 	  Boot an ELF/vxWorks image from the memory.
 
+config CMD_FDT
+	bool "Flattened Device Tree utility commands"
+	default y
+	depends on OF_LIBFDT
+	help
+	  Do FDT related setup before booting into the Operating System.
+
 config CMD_GO
 	bool "go"
 	default y