drm/i915: Track fence region ID in plane state

drm/i915: Track fence region ID in plane state

Get rid of the needlessly complicated PLANE_HAS_FENCE +
intel_parent_vma_fence_id() dance by simply tracking the
fence_id directly in the plane state.

v2: Don't request the redundant fence for fbdev (Jani)
    Assign *out_fence_id with '=' instead of '|=' (Sashiko,Jani)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260407170942.16515-1-ville.syrjala@linux.intel.com