i440fx-test: verify firmware under 4G and 1M, both -bios and -pflash

Check whether the firmware is not hidden by other memory regions.

Qemu is started in paused mode: it shouldn't try to interpret generated
garbage.

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
