This was used to track which hart a given operation must apply to. But
we already have a target associated with each operation, and from there
we can find the desired hart id. dm013_info_t already tracks
current_hartid (meaning which hart ID is currently selected by the DM).
This makes the code simpler to understand. Also it turns out we don't
need to make sure the correct hart ID is currently selected because
there are only a few real entry points.
Change-Id: Ibe8d5e156523397f245edd6ec0a5df3239b717bf
Signed-off-by: Tim Newsome <tim@sifive.com>