Currently the all the slot processing for the completion queue is done
in ISR context. It is judged that the slot processing can take a long
time, especially when a SATA NCQ completes (upto 32 slots).

So, as a solution, defer the bulk of the ISR processing to tasklet
context. Each CQ will have its down tasklet.
Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Xiang Chen <chenxiang66@hisilicon.com>
Reviewed-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>