Added DRV8461SPWP SPI-controlled 3A stepper motor controller
This is TI's answer to Trinamic :-) This MR only adds the SPI-controlled variant (these are not pin alternatives but for the 28-pin package these are separate parts) and only adds the 28-pin PWP package.
- VREF at the top to facilitate resistor divider from DVDD/VCC
- CPL/CHP/VCP are charge pump (Gate driver) connections, with space for a C_small. They are set to Input so the ERC complains.