net: hns3: uninitialize command queue while unloading PF driver

According to the hardware's description, the driver should clear
the command queue's registers when uloading driver. Otherwise,
these existing value may lead the IMP get into a wrong state.

Also this patch adds hclge_cmd_uninit() to do the command queue
uninitialization which includes clearing registers and freeing
memory.

Fixes: 68c0a5c7

 ("net: hns3: Add HNS3 IMP(Integrated Mgmt Proc) Cmd Interface Support")
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>