Merge branch 'Add USDT support for s390'

Ilya Leoshkevich says:

====================

This series adds USDT support for s390, making the "usdt" test pass
there. Patch 1 is a collection of minor cleanups, patch 2 adds
BPF-side support, patch 3 adds userspace-side support.
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>