qdev: Use clz in print_size

We can compute a floor log2 value with clz rather than a division loop.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Message-id: 1375208443-17288-3-git-send-email-rth@twiddle.net
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
