arch: score: Export necessary symbols in related files

'csum_partial_copy_from_user' and 'flush_dcache_page' are also needed by
outside modules, so need export them in the related files.

The related error (with allmodconfig under score):

    MODPOST 1365 modules
  ERROR: "csum_partial_copy_from_user" [net/rxrpc/af-rxrpc.ko] undefined!
  ERROR: "flush_dcache_page" [net/sunrpc/sunrpc.ko] undefined!

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