drm/i915/tgl: Move and restrict Wa_1408615072

Following the changes in the previous patch
"drm/i915/gen11: Moving WAs to rcs_engine_wa_init()" also moving TGL
Wa_1408615072 to rcs_engine_wa_init() this way after a engine
reset it will be reapplied also restricting it to A0 as it is fixed in
B0 stepping.

BSpec: 52890
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200302231421.224322-2-jose.souza@intel.com