Add "get by offset" DT helpers

Add new helper functions to read a DT property by its offset. This is
useful when the property's name is unknown, e.g. when iterating through
all properties of a node.

Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Change-Id: Ia042905be6de1df545934d76fa8010bb7a2e3f17
diff --git a/components/common/fdt/fdt_helpers.h b/components/common/fdt/fdt_helpers.h
index e3fc8fc..66535ca 100644
--- a/components/common/fdt/fdt_helpers.h
+++ b/components/common/fdt/fdt_helpers.h
@@ -8,3 +8,5 @@
 
 bool dt_get_u32(const void *fdt, int node, const char *prop_name, uint32_t *prop_val);
 bool dt_get_u64(const void *fdt, int node, const char *prop_name, uint64_t *prop_val);
+bool dt_get_u32_by_offset(const void *fdt, int offset, const char **prop_name, uint32_t *prop_val);
+bool dt_get_u64_by_offset(const void *fdt, int offset, const char **prop_name, uint64_t *prop_val);