iommu: Track iopf group instead of last fault

Previously, before a group of page faults was passed to the domain's iopf
handler, the last page fault of the group was kept in the list of
iommu_fault_param::faults. In the page fault response path, the group's
last page fault was used to look up the list, and the page faults were
responded to device only if there was a matched fault.

The previous approach seems unnecessarily complex and not performance
friendly. Put the page fault group itself to the outstanding fault list.
It can be removed in the page fault response path or in the
iopf_queue_remove_device() path. The pending list is protected by
iommu_fault_param::lock. To allow checking for the group's presence in
the list using list_empty(), the iopf group should be removed from the
list with list_del_init().

IOMMU_PAGE_RESP_PASID_VALID is set in the code but not used anywhere.
Remove it to make the code clean. IOMMU_PAGE_RESP_PASID_VALID is set
in the response message indicating that the response message includes
a valid PASID value. Actually, we should keep this hardware detail in
the individual driver. When the page fault handling framework in IOMMU
and IOMMUFD subsystems includes a valid PASID in the fault message, the
response message should always contain the same PASID value. Individual
drivers should be responsible for deciding whether to include the PASID
in the messages they provide for the hardware.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://lore.kernel.org/r/20240212012227.119381-15-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

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