This patch adds firmware to the machine options.  -bios <file> becomes a
shortcut for -machine firmware=<file>.  Advantage is that the firmware
can be specified via config file as -machine is parsed using QemuOpts
and it is also possible to use different defaults for different
machine types (via QEMUMachine->default_machine_opts).
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>