drivers: stepper: update drivers as per the api changes

This commit deprecates passing of async signal in functions such as move
and set_target_position. As per the new API, the async signal has to be
set via set_async_signal.

If RAMPSTAT_POLL is activated then enable_constant_velocity_mode would be
able to raise signals like END_STOP_DETECTED & SENSORLESS_STALL_DETECTED.
This commit also adjusts shell script in order to test these signals.

Signed-off-by: Jilay Pandya <jilay.pandya@zeiss.com>