arch/score/mm/cache.c: Export 'flush_icache_range'

The related error (with allmodconfig under score):

    MODPOST 1365 modules
  ERROR: "flush_icache_range" [drivers/misc/lkdtm.ko] undefined!

Acked-by: Lennox Wu <lennox.wu@gmail.com>
Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>