disas/libvixl: Update to upstream VIXL 1.5

Update our copy of libvixl to upstream's 1.5 release.
This includes the upstream versions of the fixes we
were carrying locally (commit ffebe899).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1407162987-4659-1-git-send-email-peter.maydell@linaro.org

disas/libvixl/utils.cc

@@ -124,4 +124,14 @@ int CountSetBits(uint64_t value, int width) {
 
   return value;
 }
+
+
+uint64_t LowestSetBit(uint64_t value) {
+  return value & -value;
+}
+
+
+bool IsPowerOf2(int64_t value) {
+  return (value != 0) && ((value & (value - 1)) == 0);
+}
 }  // namespace vixl