allwinner: Constify data structures

This maximizes the amount of data protected by the MMU.

Signed-off-by: Samuel Holland <samuel@sholland.org>
diff --git a/plat/allwinner/common/sunxi_topology.c b/plat/allwinner/common/sunxi_topology.c
index 7acc77a..45be1e0 100644
--- a/plat/allwinner/common/sunxi_topology.c
+++ b/plat/allwinner/common/sunxi_topology.c
@@ -9,7 +9,7 @@
 #include <arch.h>
 #include <plat/common/platform.h>
 
-static unsigned char plat_power_domain_tree_desc[PLAT_MAX_PWR_LVL + 1] = {
+static const unsigned char plat_power_domain_tree_desc[PLAT_MAX_PWR_LVL + 1] = {
 	/* One root node for the SoC */
 	1,
 	/* One node for each cluster */