soc/cores/code_8b10b: add K helper.

litex/soc/cores/code_8b10b.py

@@ -28,6 +28,9 @@ from litex.soc.interconnect import stream
 
 # Helpers ------------------------------------------------------------------------------------------
 
+def K(x, y):
+    return (y << 5) | x
+
 def disparity(word, nbits):
     n0 = 0
     n1 = 0