drm/i915: Enable fastboot by default on Skylake and newer

We really want to have fastboot enabled by default to avoid an ugly
modeset during boot.

Rather then enabling it everywhere, lets start with enabling it on
Skylake and newer.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190124130114.3967-1-maarten.lankhorst@linux.intel.com