qapi: generate C types for fixed-width integers

(Long line folded using parens:
<http://www.python.org/dev/peps/pep-0008/#maximum-line-length

>.)

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>