Revert "drm/i915/tgl/psr: Fix glitches when doing frontbuffer modifications"

This reverts commit 71c1a499.

The proper fix is Wa_14013723622, so now we can revert this WA and
get back some power savings.

Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Tested-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210408204917.254272-2-jose.souza@intel.com