Build scripts: Adjust date time design version generation.

Ensure version generated from date time is below 0xFFFF to prevent
modulo 65536 of the generated value causing failure to work out the time at
which the design was generated.

build-bitstream.py

@@ -301,7 +301,7 @@ def get_design_version(source_list):
     if unique_design_version is None:
         now = datetime.datetime.now()
         day_of_year = now.timetuple().tm_yday
-        design_version = (day_of_year * 1440) + (now.hour * 60) + now.minute
+        design_version = ((day_of_year %45) * 1440) + (now.hour * 60) + now.minute
     else:
         try:
             udv_sl = unique_design_version.split(".")