drm/i915/skl: Implement WaDisableHBR2

v2: Use the recently introduced INTEL_REVID() and SKL_REVID defines
    (Nick Hoath)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89554


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>