drm/ttm: recognize ARM arch in ioprot handler

Nouveau can now be used on ARM, so add an ioprot handler for this
architecture.

Signed-off-by: Lucas Stach <[e-mail]>
Signed-off-by: Alexandre Courbot <[e-mail]>
Signed-off-by: David Herrmann <[e-mail]>

drivers/gpu/drm/ttm/ttm_bo_util.c

···
 			pgprot_val(tmp) |= _PAGE_GUARDED;
 	}
 #endif
-#if defined(__ia64__)
+#if defined(__ia64__) || defined(__arm__)
 	if (caching_flags & TTM_PL_FLAG_WC)
 		tmp = pgprot_writecombine(tmp);
 	else