uio: Add SVA support for PCI devices via uio_pci_generic_sva.c

This patch introduces a new UIO driver, uio_pci_generic_sva, which
extends the functionality of uio_pci_generic by adding support for
Shared Virtual Addressing (SVA) when IOMMU is enabled in the system.

The key enhancement allows PCI devices to directly use user-space virtual
addresses for DMA operations, eliminating the need for bounce buffers or
explicit IOVA mapping. This is achieved by leveraging the kernel's IOMMU-SVA
subsystem, including process address space attachment, page fault handling,
and shared context management between CPU and device.

With this driver, userspace applications can perform zero-copy DMA using
native pointers:

   void *addr = malloc(N);
   set_dma_addr((uint64_t)addr);  // Passing user VA directly
   start_dma();

The device can now access 'addr' through the IOMMU's PASID-based translation,
provided that the underlying IOMMU hardware (e.g., Intel VT-d 3.1+, AMD-Vi,
ARM SMMU, RISCV IOMMU) and platform support SVA.

Dependencies:
- CONFIG_IOMMU_SVA must be enabled.
- The platform must support PRI (Page Request Interface) and PASID.
- Device drivers/userspace must handle page faults if demand-paging is used.

The implementation reuses core logic from uio_pci_generic.c while adding
PASID setting, and integration with the IOMMU SVA APIs.

Also, add a read-only sysfs attribute 'pasid' to expose the Process Address
Space ID assigned by IOMMU driver when binding an SVA-enabled device.
For details, refer to the ABI documentation for uio_pci_sva driver sysfs attribute
(Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid).

Signed-off-by: Yaxing Guo <guoyaxing@bosc.ac.cn>
Link: https://patch.msgid.link/20250926095828.506-1-guoyaxing@bosc.ac.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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