hwmon: (dell-smm) Disable fan support for Dell Inspiron 7720

Calling fan related SMM functions implemented by Dell BIOS firmware on Dell
Inspiron 7720 freeze kernel for about 500ms. Until Dell fixes it we need to
disable fan support for Dell Inspiron 7720 as it makes system unusable.

Via "force" module param fan support can be enabled.

Reported-by:  <vova7890@mail.ru>
Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=195751
Cc: stable@vger.kernel.org # v4.0+, will need backport
Signed-off-by: Guenter Roeck <linux@roeck-us.net>