Remove sleepable kfuncs from non-sleepable program type references

[dylandreimerink]

This stackoverflow issue pointed out that we currently do not account of the sleepability of kfuncs when generating our kfunc <-> program type lists.

It would be nice if we could make the reference generation tool smart enough to know which program types cannot be sleepable and to filter out kfuncs with the KF_SLEEPABLE flag, both for the kfunc -> program type and program type -> kfunc references.