When a CPU has no scache, the scache flushing functions currently
aren't getting initialized and the NULL pointer is eventually called
as a function.  Initialize the scache flushing functions as a noop
when there's no scache.
    
Initial patch by me and most of the debugging done by Martin Michlmayr.
Signed-off-by: NMartin Michlmayr <tbm@cyrius.com>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>