[llvm] [AArch64][SME] Zero reserved bytes when allocating a new TPIDR2 object (PR #68411)

[Sander de Smalen via llvm-commits]

https://github.com/sdesmalen-arm approved this pull request.

Thanks for fixing, this zeroing was still missing and led to some runtime failures when I tried to test the compiler-rt routines https://reviews.llvm.org/D154045.

LGTM

https://github.com/llvm/llvm-project/pull/68411