[PYNQ] start adding SynthPYNQProject transform

src/finn/transformation/fpgadataflow/synth_pynq_proj.py

+import os
+import subprocess
+
+from finn.transformation import Transformation
+
+
+class SynthPYNQProject(Transformation):
+    """Run synthesis for the PYNQ project for this graph. The MakePYNQProject
+    transformation must be applied prior to this transformation."""
+
+    def __init__(self):
+        super().__init__()
+
+    def apply(self, model):
+        vivado_pynq_proj_dir = model.get_metadata_prop("vivado_pynq_proj")
+        if vivado_pynq_proj_dir is None or (not os.path.isdir(vivado_pynq_proj_dir)):
+            raise Exception("No synthesis project, apply MakePYNQProject first.")
+        synth_project_sh = vivado_pynq_proj_dir + "/synth_project.sh"
+        if not os.path.isfile(synth_project_sh):
+            raise Exception("No synthesis script, apply MakePYNQProject first.")
+        bash_command = ["bash", synth_project_sh]
+        process_compile = subprocess.Popen(bash_command, stdout=subprocess.PIPE)
+        process_compile.communicate()
+        # TODO set bitfile attribute
+        # TODO pull out synthesis statistics and put them in as attributes
+        return (model, False)