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

Lenovo Legion Y720-15IKB is another Lenovo model without a
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>