c6x: platforms: cache: Export symbol L1P_cache_block_invalidate and L1D_cache_block_writeback

They are needed by other modules, the related error with allmodconfig:

    MODPOST 3327 modules
  ERROR: "L1P_cache_block_invalidate" [drivers/misc/lkdtm.ko] undefined!
  ERROR: "L1D_cache_block_writeback" [drivers/misc/lkdtm.ko] undefined!

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: Mark Salter <msalter@redhat.com>