[util] Add constexpr log2/is_pow2 helpers

I didn't end up using these, but constexpr log2 and is_pow2 functions
might be helpful.

src/libraries/util/include/util/util.h

@@ -6,6 +6,14 @@
 
 namespace util {
 
+constexpr size_t const_log2(size_t n) {
+    return n < 2 ? 1 : 1 + const_log2(n/2);
+}
+
+constexpr bool is_pow2(size_t n) {
+    return (n & (n-1)) == 0;
+}
+
 // Get the base-2 logarithm of i
 inline unsigned log2(uint64_t i) {
     if (i < 2) return 0;