drm/xe/gt: Extract emit_job_sync()

drm/xe/gt: Extract emit_job_sync()

Both the nop and wa jobs are going through the same boiler plate calls
to emit the job with a timeout and handling error for both bb and job.
Extract emit_job_sync() so those functions create the bb, handling
possible errors and delegate the part about really emitting the job
and waiting for its completion.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Link: https://lore.kernel.org/r/20250710-lrc-refactors-v2-3-a5e2ca03f6bd@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>