drm/i915/tgl: Add note to Wa_1607297627

Add note about the confliting information in BSpec about this WA.

BSpec: 52890
Acked-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200227220101.321671-5-jose.souza@intel.com