ARM: fix const declaration of platform struct

As Julien pointed out the other day, the data type for the platform
DT name match struct is wrong.
To be really immutable, we have to use "const char * const".

Fix it on the three currently existing platforms.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

xen/arch/arm/platforms/exynos5.c

@@ -86,7 +86,7 @@ static uint32_t exynos5_quirks(void)
     return PLATFORM_QUIRK_DOM0_MAPPING_11;
 }
 
-static const char const *exynos5_dt_compat[] __initdata =
+static const char * const exynos5_dt_compat[] __initdata =
 {
     "samsung,exynos5250",
     NULL

xen/arch/arm/platforms/midway.c

@@ -41,7 +41,7 @@ static void midway_reset(void)
     iounmap(pmu);
 }
 
-static const char const *midway_dt_compat[] __initdata =
+static const char * const midway_dt_compat[] __initdata =
 {
     "calxeda,ecx-2000",
     NULL

xen/arch/arm/platforms/vexpress.c

@@ -119,7 +119,7 @@ static void vexpress_reset(void)
     iounmap(sp810);
 }
 
-static const char const *vexpress_dt_compat[] __initdata =
+static const char * const vexpress_dt_compat[] __initdata =
 {
     "arm,vexpress",
     NULL