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/src/fdt_handler.c b/src/fdt_handler.c
index 851facd..c29a0e2 100644
--- a/src/fdt_handler.c
+++ b/src/fdt_handler.c
@@ -232,7 +232,7 @@
 		goto out_unmap_fdt;
 	}
 
-	p->kernel_arg = (size_t)fdt;
+	p->kernel_arg = (uintreg_t)fdt;
 	ret = true;
 
 out_unmap_fdt: