drm/i915: Remove some local 'mode_changed' bools

These 'mode_changed' booleans aren't very helpful. Just
replace them with direct intel_crtc_needs_modeset() calls
which is more descriptive.

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/20221021162442.27283-3-ville.syrjala@linux.intel.com