[PyCDE][Handshake] Add bindings for Handshake functions

[teqdruid]

Exposes the Handshake dialect's FuncOp in the same style as an HWModuleOp:

class TestFunc(Func):
  a = Input(Bits(8))
  x = Output(Bits(8))

  @generator
  def build(ports):
    ports.x = ports.a & Bits(8)(0xF)

And instantiates them via ESI channels:

class Top(Module):
  clk = Clock()
  rst = Input(Bits(1))

  a = Input(Channel(Bits(8)))
  x = Output(Channel(Bits(8)))

  @generator
  def build(ports):
    test = TestFunc(clk=ports.clk, rst=ports.rst, a=ports.a)
    ports.x = test.x

[teqdruid]

@mikeurbach You might be interested in this.

[mikeurbach]

Very cool!

[mortbopet]

LGTM modulo "locking things down" and only allowing comb and handshake operations inside the Func (... for now).

[teqdruid]

LGTM modulo "locking things down" and only allowing comb and handshake operations inside the Func (... for now).

The reason I didn't is that I'm not quite sure the best way to do this. I don't want the signals module to know about the handshake module... so I'd have to create a new infrastructure for the containing module to hook into any operation creation to validate or override it. I think that's a bit too much for this PR. Unless you have any suggestions for a simpler way to do this...?