[linux-kernel] Update patches for v2

* Reduce stack usage of many zstd functions, none use over 388 B anymore.
* Remove an incorrect `const` in `xxhash`.

contrib/linux-kernel/test/include/linux/math64.h

@@ -0,0 +1,11 @@
+#ifndef LINUX_MATH64_H
+#define LINUX_MATH64_H
+
+#include <stdint.h>
+
+static uint64_t div_u64(uint64_t n, uint32_t d)
+{
+  return n / d;
+}
+
+#endif