drm/ttm: recognize ARM64 arch in ioprot handler

Return proper pgprot for ARM64. This is required for objects like
Nouveau fences to be mapped with expected coherency.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -490,7 +490,8 @@ pgprot_t ttm_io_prot(uint32_t caching_flags, pgprot_t tmp)
 	else if (boot_cpu_data.x86 > 3)
 		tmp = pgprot_noncached(tmp);
 #endif
-#if defined(__ia64__) || defined(__arm__) || defined(__powerpc__)
+#if defined(__ia64__) || defined(__arm__) || defined(__aarch64__) || \
+    defined(__powerpc__)
 	if (caching_flags & TTM_PL_FLAG_WC)
 		tmp = pgprot_writecombine(tmp);
 	else