[PATCH v2 1/3] arm64/sme: Support disabling streaming mode via ptrace on SME only systems

[David Spickett]

I have put the LLDB changes for this into review.
We are tracking SME only support in this issue:
https://github.com/llvm/llvm-project/issues/138717

The PRs that relate to these kernel changes are
listed in this comment:
https://github.com/llvm/llvm-project/issues/138717#issuecomment-3456979166

LLDB's use case for this new ptrace feature is to restore
process state after expression evaluation takes a process
from non-streaming to streaming mode. We have a specific
code path to handle that restoration, and it was not a
problem to integrate this new ptrace feature.

I have proven with testcases that LLDB can restore
any streaming mode/ZA/streaming vector length
combination, starting from any other combination.

The LLDB changes will remain in review until if/when
these kernel changes are accepted. I expect LLDB
reviewers will be ok approving changes on the condition
that I wait for the kernel side before merging.

I expect LLDB review to take some time, likely a month,
due to the availability of reviewers at this time.

Reviewed-by: David Spickett <david.spickett at linaro.org>