Automatically set folding attributes (#251)

* Added transform and test for auto-folding to throughput target

* [SetFolding] improve comments

* [SetFolding] allow customizing mvau_wwidth_max

* [SetFolding] put ops into groups to reduce code redundancy

* [SetFolding] add a two-pass relaxation option

* [LabelSelect] implement get_exp_cycles

* [SetFolding] handle LabelSelect too

* [SetFolding] extra comment

* [SetFolding] fix swg setting, add warning

* [SetFolding] call GiveUniqueNodeNames before AnnotateCycles

* [Build] add build config option to target FPS

* [Test] use target_fps for example dataflow build config file

Co-authored-by: Yaman Umuroglu <yamanu@xilinx.com>