include: kernel: arch: sys: Use new TLS macro

PR #78645 replaced uses of the GNU keyword `__thread` with a new macro
`Z_THREAD_LOCAL` which expands to correspond C/C++ standard keyword if
applicable, else it falls back to `__thread`.

This PR addresses some missed replacements in headers files for #78645.

Signed-off-by: Daniel Flodin <daniel.flodin@iar.com>