drm/i915/tgl: Add Wa_1409825376 to tgl

Workaround database indicates we should disable VRH clockgating
in pre-production hardware.

V2:
 - Use REG_BIT macro
 - Update reference in commit message(Matt)

Bspec: 52890
Bspec: 49424
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200109223727.5630-1-radhakrishna.sripada@intel.com