device_tree: Add support for reading device tree properties

Add support for reading device tree properties (both generic
and single-cell ones) to QEMU's convenience wrapper layer.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter A. G. Crosthwaite <peter.crosthwaite@petalogix.com>
diff --git a/device_tree.h b/device_tree.h
index 2244270..f7a3e6c 100644
--- a/device_tree.h
+++ b/device_tree.h
@@ -28,6 +28,10 @@
 int qemu_devtree_setprop_phandle(void *fdt, const char *node_path,
                                  const char *property,
                                  const char *target_node_path);
+const void *qemu_devtree_getprop(void *fdt, const char *node_path,
+                                 const char *property, int *lenp);
+uint32_t qemu_devtree_getprop_cell(void *fdt, const char *node_path,
+                                   const char *property);
 uint32_t qemu_devtree_get_phandle(void *fdt, const char *path);
 uint32_t qemu_devtree_alloc_phandle(void *fdt);
 int qemu_devtree_nop_node(void *fdt, const char *node_path);