Revert "lz4: Squash sync with stable lz4"

This reverts commit ac6a2c778308230c8540f0c696ec789cb4d390ac.
Revert "smp: Add generic smpboot facility"

This reverts commit 6e6dcb55480093745f94de412804393977792ed2.
Revert "rcu: Yield simpler"

This reverts commit 7d3d93f74cee297d5aa2aea0d6dfb4610c5c77bb.