platform/x86: ideapad-laptop: Add Y720-15IKBN to no_hw_rfkill

Lenovo Legion Y720-15IKBN is yet another Lenovo model that does not
have an hw rfkill switch, resulting in wifi always reported as hard
blocked.

Add the model to the list of models without rfkill switch.

Signed-off-by: Olle Liljenzin <olle@liljenzin.se>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>