drm/xe/gt_pagefault: Print engine class string

drm/xe/gt_pagefault: Print engine class string

The engine class index which is printed here is an internal representation
for debugging. It is _not_ an index based on DRM_XE_ENGINE_CLASS_* values
provided in the uAPI. Add the string representation of the engine class to
the output in order to limit possible confusion by users when analyzing the
logs.

Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250129175241.338043-1-francois.dugast@intel.com
Signed-off-by: Francois Dugast <francois.dugast@intel.com>