drm/i915/tgl: Make Wa_1606700617 permanent

This workaround is to disable FF DOP Clock gating. The fix
in B0 was backed out due to timing reasons and decided to
be made permanent.

Bspec: 52890
Signed-off-by: Swathi Dhanavanthri <swathi.dhanavanthri@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200305181204.28856-1-swathi.dhanavanthri@intel.com