drm/xe: Fix build without debugfs

When CONFIG_DEBUG_FS is off, drivers/gpu/drm/xe/xe_gt_debugfs.o
is not built and build fails on some setups with:

	ld: drivers/gpu/drm/xe/xe_gt.o: in function `xe_fault_inject_gt_reset':
	drivers/gpu/drm/xe/xe_gt.h:27:(.text+0x1659): undefined reference to `gt_reset_failure'
	ld: drivers/gpu/drm/xe/xe_gt.h:27:(.text+0x1c16): undefined reference to `gt_reset_failure'
	collect2: error: ld returned 1 exit status

Do not use the gt_reset_failure attribute if debugfs is not enabled.

Fixes: 8f3013e0 ("drm/xe: Introduce fault injection for gt reset")
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://lore.kernel.org/r/20250722-xe-fix-build-fault-v1-1-157384d50987@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>