Add swish

[AdamCuellar]

I've added swish for yolov4-csp-swish and yolov4-csp-x-swish from Darknet

I don't have a Xavier or Nano to test on but for V100:

FP32:
75.49 AVG FPS for yolov4-csp-swish
50.99 AVG FPS for yolov4-csp-x-swish

FP16:
111.95 AVG FPS for yolov4-csp-swish
78.14 AVG FPS for yolov4-csp-x-swish

[mive93]

Hi @AdamCuellar,

I don't know why I missed this.
I will look into it next week, test it on embedded boards, and in case merge it.
Thank you.

[harsco-jfernandez]

Hi,

Any reason why the swish implementation from @AdamCuellar hasn't been merged yet? It would be nice to have that available even tho I could replace swish with mish, but there are some advantages to swish.

Thanks.