Add support to gf180mcu-pdk

[mohamedleithy]

DFFRAM should be pdk generic to support gf180mcu-pdk.

[xobs]

What needs to be done in order to do this? Has any work been started?

I've started writing a block_definitions.v, but it's complicated somewhat by the different cells. For example, I need to add inverters in order to get DEC1x2 working. And diodes aren't quite the same. And because of the difference in cell composition, there are subtle changes that need to be made to various python bits.