dm: core: Add a place to put extra device-tree reading functions

Some functions deal with structured data rather than simple data types.
It makes sense to have these in their own file. For now this just has a
function to read a flashmap entry. Move the data types also.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/cros_ec.h b/include/cros_ec.h
index 0271f2b..2bd9f22 100644
--- a/include/cros_ec.h
+++ b/include/cros_ec.h
@@ -14,6 +14,7 @@
 #include <fdtdec.h>
 #include <cros_ec_message.h>
 #include <asm/gpio.h>
+#include <dm/of_extra.h>
 
 /* Our configuration information */
 struct cros_ec_dev {