drm/xe: Select CONFIG_DEVICE_PRIVATE when DRM_XE_GPUSVM is selected

drm/xe: Select CONFIG_DEVICE_PRIVATE when DRM_XE_GPUSVM is selected

CONFIG_DEVICE_PRIVATE is a prerequisite for DRM_XE_GPUSVM.
Explicitly select it so that DRM_XE_GPUSVM is not unintentionally
left out from distro configs not explicitly enabling
CONFIG_DEVICE_PRIVATE.

v2:
- Select also CONFIG_ZONE_DEVICE since it's needed by
  CONFIG_DEVICE_PRIVATE.
v3:
- Depend on CONFIG_ZONE_DEVICE rather than selecting it.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: <dri-devel@lists.freedesktop.org>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patch.msgid.link/20260121091048.41371-3-thomas.hellstrom@linux.intel.com
(cherry picked from commit 9386f49316074d2d76fd78d6bd359996de42fb7f)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>