pdbg: Call thread_<op>_all() api if all threads are selected
pdbg: Call thread_<op>_all() api if all threads are selected

This allows to optimize the thread operations (start/step/stop/sreset)
when using sbefifo backend.

Signed-off-by: Amitay Isaacs <a505e7c038746dbeb3edcd8d146dbd515432801f@ozlabs.org>

open-power/pdbg,open-power/pdbg,open-power/pdbg