drm/i915: Gen9 shadowed registers

For MMIO registers which are shadowed, force wake is not needed to
write to these registers.

v2: Rebase on top of nightly (Damien)

v3: Rebase on top of "Gen9 multiple-engine forcewake" changes

v4: (Mika, Bob, done by Damien)
- Reorder the shadowed registers by popularity

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Zhe Wang <zhe1.wang@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>