drm/i915: Enable atomic by default on ctg/elk

The watermark code for ctg/elk has been atomic ready for a long time
so let's just flip the switch now that some of the last CxSR issues
have been sorted out (which granted was a problem for vlv/chv as well
despite them already having atomic enabled by default).

v2: Rebase

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221007211108.3883-2-ville.syrjala@linux.intel.com


Acked-by: Jani Nikula <jani.nikula@intel.com>