Connect Step/Direction signals on PandABrick encoders development branch

[tomtrafford]

Currently in the PandABrick-encoders branch, the STEP and DIRECTION signals of the pmacenc block have been disabled. They need to be enable, to do this:

• Un-comment their fields in pmacenc.block.ini (modules>>pmacenc). The autogen framework will automatically add them to the ctrl blocks.
• Connect the signals from the pmacenc_ctrl block instatintaion in PandABrick_encoders_block.vhd (targets>>PandABrick>>hdl) to the PandABrick_encoders instantiation. And add them to the PandABrick_encoders port map (PandABrick_encoders.vhd).
• The signals are on the bit bus so they need to be added in PandABrick_top.vhd (targets>>PandABrick>>hdl). This will need wiring through PandABrick_encoders_top.vhd.
• These will need to replace the existing signals: step, dir within the PandABrick_encoders.vhd