drm/i915: Assert that VRR is off during vblank evasion if necessary

drm/i915: Assert that VRR is off during vblank evasion if necessary

Whenever we change the actual transcoder timings (clock via
seamless M/N, full modeset, (or soon) vtotal via LRR) we
want the timing generator to be in non-VRR during the commit.
Warn if we forgot to turn VRR off prior to vblank evasion.

Cc: Manasi Navare <navaremanasi@chromium.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901130440.2085-12-ville.syrjala@linux.intel.com
Reviewed-by: Manasi Navare <navaremanasi@chromium.org>
Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>