drm/xe: add kdev_to_xe_device() helper and use it

There are enough users for kernel device to xe device conversion, add a
helper for it.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/38c80846e70c7e410850530426384e17cff9d031.1723458544.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>