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_common.c b/plat/allwinner/common/sunxi_common.c
index 6bb8968..3b44aab 100644
--- a/plat/allwinner/common/sunxi_common.c
+++ b/plat/allwinner/common/sunxi_common.c
@@ -18,7 +18,7 @@
 #include <sunxi_mmap.h>
 #include <sunxi_private.h>
 
-static mmap_region_t sunxi_mmap[PLATFORM_MMAP_REGIONS + 1] = {
+static const mmap_region_t sunxi_mmap[PLATFORM_MMAP_REGIONS + 1] = {
 	MAP_REGION_FLAT(SUNXI_SRAM_BASE, SUNXI_SRAM_SIZE,
 			MT_MEMORY | MT_RW | MT_SECURE),
 	MAP_REGION_FLAT(SUNXI_DEV_BASE, SUNXI_DEV_SIZE,