[CreateSiFiveMetadata] Generate firrtl.class instead of om.class

[prithayan]

Update the object model generated by the CreateSiFiveMetadata pass to generate firrtl dialect, instead of om dialect. Ensure all firrtl.class associated with the metadata are instantiated inside a top level firrtl.class SiFive_Metadata , which is instantiated inside the top level firrtl.module. This is required for ensuring that subsequent passes can lower it correctly. Generate all the hierarchical paths to the memory and associate them with the path operation for the memory metadata.