The code automatically reduces the hold_current so that it is no
greater than the run_current. However, this could lead to confusing
behavior if one reduced and then increased the run_current via
SET_TMC_CURRENT commands. To avoid that, this change adds support for
tracking the requested hold_current - thus changes to run_current
don't subtly alter the hold_current.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
86fee2d517