drm/xe: Enable CPU address mirror uAPI

Support for CPU address mirror bindings in SRAM fully in place, enable the
implementation.

v3:
 - s/system allocator/CPU address mirror (Thomas)
v7:
 - Only enable uAPI if selected by GPU SVM (CI)

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250306012657.3505757-19-matthew.brost@intel.com