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 <[e-mail]>
Cc: Matthew Brost <[e-mail]>
Cc: Rodrigo Vivi <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Thomas Hellström <[e-mail]>
Reviewed-by: Matthew Auld <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
(cherry picked from commit 9386f49316074d2d76fd78d6bd359996de42fb7f)
Signed-off-by: Thomas Hellström <[e-mail]>

drivers/gpu/drm/xe/Kconfig

···
 	bool "Enable CPU to GPU address mirroring"
 	depends on DRM_XE
 	depends on !UML
-	depends on DEVICE_PRIVATE
+	depends on ZONE_DEVICE
 	default y
+	select DEVICE_PRIVATE
 	select DRM_GPUSVM
 	help
 	  Enable this option if you want support for CPU to GPU address