[MIPS] sc-rm7k.c cleanup

    
Use blast_scache_range, blast_inv_scache_range for rm7k scache routine.
Output code should be logically same.
    
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>