[efi] Create a copy of the system flattened device tree, if present

EFI configuration tables may be freed at any time, and there is no way
to be notified when the table becomes invalidated.  Create a copy of
the system flattened device tree (if present), so that we do not risk
being left with an invalid pointer.

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

src/core/fdt.c

@@ -456,8 +456,7 @@ int fdt_mac ( struct fdt *fdt, unsigned int offset,
  * @v max_len		Maximum device tree length
  * @ret rc		Return status code
  */
-int fdt_parse ( struct fdt *fdt, const struct fdt_header *hdr,
-		size_t max_len ) {
+int fdt_parse ( struct fdt *fdt, struct fdt_header *hdr, size_t max_len ) {
 	const uint8_t *end;
 
 	/* Sanity check */