Hi,
this is a small cleanup of kfifo.
More importantly, it introduces three helpers: kfifo_skip_count(),
kfifo_out_linear() and kfifo_out_linear_ptr(). They allow using kfifo in
the serial layer.
They are needed as up to now, there is no way to "peek" the data without
actually copying to a temporary buffer. kfifo_out_linear*() allow that
and kfifo_skip_count() then allows for tail moving after the copy is
done. Note the copy is usually performed directly to hardware e.g. via
outb(), hence the need for peek without copying anywhere.