Add %ctest timeout on riscv64
    
    Since our riscv64 builders are slow at the moment some tests fail with
    timeouts, eg:
    https://src.fedoraproject.org/rpms/kokkos/pull-request/11
    
    Adding the --timeout flag on riscv64 only increases the timeout and
    makes the tests pass.  Adding this centrally makes it easier to remove
    it later once faster hardware becomes widely available.
    
    Signed-off-by: Richard W.M. Jones <rjones@redhat.com>