sched_ext: Rename scx_kfunc_set_sleepable to unlocked and relocate

Sleepables don't need to be in its own kfunc set as each is tagged with
KF_SLEEPABLE. Rename to scx_kfunc_set_unlocked indicating that rq lock is
not held and relocate right above the any set. This will be used to add
kfuncs that are allowed to be called from SYSCALL but not TRACING.

No functional changes intended.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>