Significant change to Stepper motor device behaviour, using devcb2 interfaces.

New functions added:

 MCFG_STEPPER_ADD(tag) - add a stepper device
 MCFG_STEPPER_REEL_TYPE(type) - the equivalent of the first line in the old interface, now also takes NOT_A_REEL for printer and similar applications
 MCFG_STEPPER_START_INDEX(int index) - the old second line of the interface, the position (in half steps) where the optic tab first triggers.
 MCFG_STEPPER_END_INDEX(int index)  - the old third line of the interface, the last position (in half steps) where the optic tab triggers.
 MCFG_STEPPER_INDEX_PATTERN(int pattern) - a coil pattern in hexadecimal that has to be on the motor for the index to trigger (0 if no specific pattern is needed)
 MCFG_STEPPER_INIT_PHASE(int phase) - starting phase of the motor

All drivers have been updated, testing done to all specific drivers - Scorpion 4 was particularly complex. [James Wallace]