binman: Automatically expand phase binaries into sections

When creating an entry, check for an expanded version of that entry, then
use it instead. This allows, for example use of:

   u-boot {
   };

instead of having to write out in full:

   u-boot {
      type = "section";

      u-boot-nodtb {
      };

      u-boot-dtb {
      };
   };

Add an implementaion of this and associated documentation.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/test/195_fdt_incl_tpl.dts b/tools/binman/test/195_fdt_incl_tpl.dts
new file mode 100644
index 0000000..3756ac4
--- /dev/null
+++ b/tools/binman/test/195_fdt_incl_tpl.dts
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/dts-v1/;
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	binman {
+		u-boot-tpl {
+		};
+	};
+};