drm/xe/uapi: Add UAPI support for purgeable buffer objects

drm/xe/uapi: Add UAPI support for purgeable buffer objects

Extend the DRM_XE_MADVISE ioctl to support purgeable buffer object
management by adding DRM_XE_VMA_ATTR_PURGEABLE_STATE attribute type.

This allows userspace applications to provide memory usage hints to
the kernel for better memory management under pressure:

- WILLNEED: Buffer is needed and should not be purged. If the BO was
  previously purged, retained field returns 0 indicating backing store
  was lost (once purged, always purged semantics matching i915).

- DONTNEED: Buffer is not currently needed and may be purged by the
  kernel under memory pressure to free resources. Only applies to
  non-shared BOs.

  To prevent undefined behavior, the following operations are blocked
  while a BO is in DONTNEED state:
  - New mmap() operations return -EBUSY
  - VM_BIND operations return -EBUSY
  - New dma-buf exports return -EBUSY
  - CPU page faults return SIGBUS
  - GPU page faults fail with -EACCES

  This ensures applications cannot use a BO while marked as DONTNEED,
  preventing erratic behavior when the kernel purges the backing store.

The implementation includes a 'retained' output field (matching i915's
drm_i915_gem_madvise.retained) that indicates whether the BO's backing
store still exists (1) or has been purged (0).

Added DRM_XE_QUERY_CONFIG_FLAG_HAS_PURGING_SUPPORT flag to allow
userspace to detect kernel support for purgeable buffer objects
before attempting to use the feature.

Cc: Matthew Brost <matthew.brost@intel.com>
Acked-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260326130843.3545241-2-arvind.yadav@intel.com