drm/i915/cnl: Add force wake for gen10+.

By spec there is no change on force wake registers
for Cannonlake. Let's reuse gen9 one.

v2: Adding missing case for the write part. (Tvrtko)
v3: Rebase on recent tree.
v4: Make it for gen9+ instead adding gen10 only. (by Joonas).

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1499302831-17773-1-git-send-email-rodrigo.vivi@intel.com