drm/xe: Add "null_sparse" type to VM snap properties

drm/xe: Add "null_sparse" type to VM snap properties

Add "null_sparse" type to VM snap properties indicating the VMA reads
zero and writes are droppped. This is useful information for debug and
will help build a robust GPU hang replay tool.

The current format is:

[<vma address>]: <permissions>|<type>

Permissions has two options, either "read_only" or "read_write".

Type has three options, either "userptr", "null_sparse", or "bo".

Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://patch.msgid.link/20251126185952.546277-3-matthew.brost@intel.com