drm/i915: Move DRRS enable/disable higher up

No reason to keep the DRRS enable/disable hidden insider the encoder
hooks. Let's just move them all the way up into platform independent
code so that all platforms get to use them. These are nops when
the state computation doesn't think DRRS is possible.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220311172428.14685-14-ville.syrjala@linux.intel.com