drm/xe: use IS_ENABLED() instead of defined() on config options

Prefer IS_ENABLED() instead of defined() for checking whether a kconfig
option is enabled.

Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240904145231.3902289-1-jani.nikula@intel.com


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