binman: Provide a way to specify the fdt-list directly

Sometimes multiple boards are built with binman and it is useful to
specify a different FDT list for each. At present this is not possible
without providing multiple values of the of-list entryarg (which is not
supported in the U-Boot build system).

Allow a fit,fdt-list-val string-list property to be used instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/entries.rst b/tools/binman/entries.rst
index b71af80..b55f424 100644
--- a/tools/binman/entries.rst
+++ b/tools/binman/entries.rst
@@ -615,6 +615,12 @@
         `of-list` meaning that `-a of-list="dtb1 dtb2..."` should be passed
         to binman.
 
+    fit,fdt-list-val
+        As an alternative to fit,fdt-list the list of device tree files
+        can be provided in this property as a string list, e.g.::
+
+            fit,fdt-list-val = "dtb1", "dtb2";
+
 Substitutions
 ~~~~~~~~~~~~~