iommu: Add a timeout parameter for PRQ response

maillist inclusion
category: feature
bugzilla: 51855
CVE: NA

Reference: https://jpbrucker.net/git/linux/commit/?h=sva/2021-03-01&id=2c56ef21daed0cd65da9b4907ce4b84c56ca7c1c



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When an I/O page request is processed outside the IOMMU subsystem,
response can be delayed or lost. Add a tunable setup parameter such that
user can choose the timeout for IOMMU to track pending page requests.

This timeout mechanism is a basic safety net which can be implemented in
conjunction with credit based or device level page response exception
handling.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Lijun Fang <fanglijun3@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>