drm/i915: Remove remaining locks from i9xx plane udpates

Now that fbc no longer nukes while a flip is pending we can
remove the last uncore.lock from the i9xx plane code.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220315140001.1172-5-ville.syrjala@linux.intel.com


Reviewed-by: Mika Kahola <mika.kahola@intel.com>