Eliminate code duplication between core_v1.c and core_v2.c by extracting
shared logic into core_common.c and unifying submit/complete handlers
through a per-queue operations vtable (struct mx_queue_ops).

Changes:
- Extract descriptor list utilities (mx_get_list_count,
  mx_get_total_desc_count, mx_desc_list_init) to core_common.c.
  The v1/v2 behavioral difference (v2 skips the first SG entry) is
  handled via skip_first/skip_first_entry parameters.
- Extract kthread_stop helper (mx_stop_queue_threads) to core_common.c.
- Add struct mx_queue_ops vtable with is_pushable, push_command,
  post_submit, is_popable, pop_completion, post_complete callbacks.
- Implement unified mx_submit_handler/mx_complete_handler in
  core_common.c that dispatch through the ops vtable.
- Add v1_queue_ops/v2_queue_ops adapter wrappers using container_of
  (safe since common is the first member in both queue structs).
- Remove duplicated submit_handler/complete_handler from both files.
- Add .clang-format to disable auto-formatting for this kernel module.