drm/xe/uapi: Move CPU_CACHING defines before doc

Move those defines to align on the rule used elsewhere in the file which
was introduced by commit 4f082f2c ("drm/xe: Move defines before
relevant fields").

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: José Roberto de Souza <jose.souza@intel.com>
Acked-by: Mateusz Naklicki <mateusz.naklicki@intel.com>
Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>