workqueue: Rename NUMA related names to use pod instead

Workqueue is in the process of improving CPU affinity awareness. It will
become more flexible and won't be tied to NUMA node boundaries. This patch
renames all NUMA related names in workqueue.c to use "pod" instead.

While "pod" isn't a very common term, it short and captures the grouping of
CPUs well enough. These names are only going to be used within workqueue
implementation proper, so the specific naming doesn't matter that much.

* wq_numa_possible_cpumask -> wq_pod_cpus

* wq_numa_enabled -> wq_pod_enabled

* wq_update_unbound_numa_attrs_buf -> wq_update_pod_attrs_buf

* workqueue_select_cpu_near -> select_numa_node_cpu

  This rename is different from others. The function is only used by
  queue_work_node() and specifically tries to find a CPU in the specified
  NUMA node. As workqueue affinity will become more flexible and untied from
  NUMA, this function's name should specifically describe that it's for
  NUMA.

* wq_calc_node_cpumask -> wq_calc_pod_cpumask

* wq_update_unbound_numa -> wq_update_pod

* wq_numa_init -> wq_pod_init

* node -> pod in local variables

Only renames. No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>