tests/libqos: Add io_fw_cfg_uninit() and mm_fw_cfg_uninit()

tests/libqos: Add io_fw_cfg_uninit() and mm_fw_cfg_uninit()

The mm_fw_cfg_init() allocates a QFWCFG object,
add mm_fw_cfg_uninit() to deallocate it.
Similarly with io_fw_cfg_init(), add io_fw_cfg_uninit().

Signed-off-by: Li Qiang <liq3ea@163.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190424140643.62457-2-liq3ea@163.com>
[PMD: Split patch, filled commit description]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>