[build] Mark FDT management tools as permitted for UEFI Secure Boot

An EFI build of iPXE does not directly make use of a flattened device
tree (FDT) itself, but may pass on a device tree that the user chose
to download using the "fdt" command.

Review the simple files used to implement the "fdt" command and mark
these as permitted for UEFI Secure Boot.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/hci/commands/fdt_cmd.c

@@ -22,6 +22,7 @@
  */
 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+FILE_SECBOOT ( PERMITTED );
 
 #include <getopt.h>
 #include <ipxe/command.h>

src/include/usr/fdtmgmt.h

@@ -8,6 +8,7 @@
  */
 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+FILE_SECBOOT ( PERMITTED );
 
 #include <ipxe/image.h>
 

src/usr/fdtmgmt.c

@@ -22,6 +22,7 @@
  */
 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+FILE_SECBOOT ( PERMITTED );
 
 #include <ipxe/fdt.h>
 #include <usr/fdtmgmt.h>