intel: Replace sprinkled intel_batchbuffer_flush with MI_FLUSH or nothing.

intel: Replace sprinkled intel_batchbuffer_flush with MI_FLUSH or nothing.

Most of these were to ensure that caches got synchronized between 2d (or meta)
rendering and later use of the target as a source, such as for texture
miptree setup.  Those are replaced with intel_batchbuffer_emit_mi_flush(),
which just drops an MI_FLUSH.  Most of the remainder were to ensure that
REFERENCES_CLIPRECTS batchbuffers got flushed before the lock was dropped.
Those are now replaced by automatically flushing those when dropping the lock.