dm: doc: add documentation for pre-reloc properties in SPL and TPL

Add documentation for the pre-reloc property in SPL and TPL device-tree:
- u-boot,dm-pre-proper
- u-boot,dm-pre-reloc
- u-boot,dm-spl
- u-boot,dm-tpl

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/dm/ofnode.h

@@ -676,12 +676,14 @@ int ofnode_read_simple_size_cells(ofnode node);
  * After relocation and jumping into the real U-Boot binary it is possible to
  * determine if a node was bound in one of SPL/TPL stages.
  *
- * There are 3 settings currently in use
- * -
+ * There are 4 settings currently in use
+ * - u-boot,dm-pre-proper: U-Boot proper pre-relocation only
  * - u-boot,dm-pre-reloc: legacy and indicates any of TPL or SPL
  *   Existing platforms only use it to indicate nodes needed in
  *   SPL. Should probably be replaced by u-boot,dm-spl for
  *   new platforms.
+ * - u-boot,dm-spl: SPL and U-Boot pre-relocation
+ * - u-boot,dm-tpl: TPL and U-Boot pre-relocation
  *
  * @node: node to check
  * @return true if node is needed in SPL/TL, false otherwise