Remove duplicate code for creating and destroying hardware contexts via
mailbox.

Link: https://lore.kernel.org/r/20220302064830.61706-7-liangwenpeng@huawei.comSigned-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>