PCI/ATS: Add PRI stubs

maillist inclusion
category: feature
bugzilla: 51855
CVE: NA

Reference: https://jpbrucker.net/git/linux/commit/?h=sva/2021-03-01&id=f61a8d9eceb10611c5f0bb151ad3dbc754bc6467



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The SMMUv3 driver, which can be built without CONFIG_PCI, will soon gain
support for PRI.  Partially revert commit c6e9aefb ("PCI/ATS: Remove
unused PRI and PASID stubs") to re-introduce the PRI stubs, and avoid
adding more #ifdefs to the SMMU driver.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Lijun Fang <fanglijun3@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>