Add ENC_POL setting to ar-usb/wou_stepgen.c

* support ENCODER POLARITY setting on INI/HAL file
* refer to araisrobo/miller/{.test.ini,miller.hal}
wou_stepgen.c: could pass ENCODER-SCALE to FPGA

* Add ENC_SCALE to motion_parameter[] for FPGA
* Remove MAX_JERK_RECIP from motion_parameter[] from FPGA
* Update configs/araisrobo/miller/.test.ini to test ENC_SCALE
  implementation