sched_ext: Relocate run_deferred() and its callees

sched_ext: Relocate run_deferred() and its callees

Previously, both process_ddsp_deferred_locals() and reenq_local() required
forward declarations. Reorganize so that only run_deferred() needs to be
declared. Both callees are grouped right before run_deferred() for better
locality. This reduces forward declaration clutter and will ease adding more
to the run_deferred() path.

No functional changes.

v2: Also relocate process_ddsp_deferred_locals() next to run_deferred()
    (Daniel Jordan).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>