Reduce the use of size_t.

Many uses have more specific types that should be used instead. In
particular, size_t was used for register sized types so uintreg_t is
introduced to be more explicit and portable.

Change-Id: Ib8038bdd9cd164e6d9b1f42d10d4b1654a665997
diff --git a/inc/hf/fdt.h b/inc/hf/fdt.h
index 14e7736..5467f7e 100644
--- a/inc/hf/fdt.h
+++ b/inc/hf/fdt.h
@@ -28,7 +28,7 @@
 };
 
 size_t fdt_header_size(void);
-size_t fdt_total_size(struct fdt_header *hdr);
+uint32_t fdt_total_size(struct fdt_header *hdr);
 void fdt_dump(struct fdt_header *hdr);
 bool fdt_root_node(struct fdt_node *node, const struct fdt_header *hdr);
 bool fdt_find_child(struct fdt_node *node, const char *child);