drm/i915/gt: Declare gen9 has 64 mocs entries!

We checked the table size against a hardcoded number of entries, and
that number was excluding the special mocs registers at the end.

Fixes: 977933b5

 ("drm/i915/gt: Program mocs:63 for cache eviction on gen9")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: <stable@vger.kernel.org> # v4.3+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201127102540.13117-1-chris@chris-wilson.co.uk