drm/i915: Whitelist context-local timestamp in the gen9 cmdparser

Allow batch buffers to read their own _local_ cumulative HW runtime of
their logical context.

Fixes: 0f2f3975

 ("drm/i915: Add gen9 BCS cmdparsing")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: <stable@vger.kernel.org> # v5.4+
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200601161942.30854-1-chris@chris-wilson.co.uk