Add c++ keywords to QAPI helper script

Add c++ keywords to avoid errors in compiling with c++ compiler.
This also renames class member of PciDeviceInfo to q_class.

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama@hds.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>