drivers: stepper: add stepper shell

Add shell commands to enable/disable, move, set velocity, configure
micro-step resolution, and display stepper motor status. Includes an
`info` command to output all relevant data with graceful handling of
unsupported features.

Signed-off-by: Jilay Pandya <jilay.pandya@outlook.com>
Signed-off-by: Fabian Blatz <fabianblatz@gmail.com>