fdt: Allow indicating a node is for U-Boot proper only

This add missing parts for previous commit 06f94461a9f4
("fdt: Allow indicating a node is for U-Boot proper only")

At present it is not possible to specify that a node should be used before
relocation (in U-Boot proper) without it also ending up in SPL and TPL
device trees. Add a new "u-boot,dm-pre-proper" boolean property for this.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/util.c b/drivers/core/util.c
index 96e47dc..60b939a 100644
--- a/drivers/core/util.c
+++ b/drivers/core/util.c
@@ -42,6 +42,8 @@
 #else
 	if (ofnode_read_bool(node, "u-boot,dm-pre-reloc"))
 		return true;
+	if (ofnode_read_bool(node, "u-boot,dm-pre-proper"))
+		return true;
 
 	/*
 	 * In regular builds individual spl and tpl handling both