This primitive allows you to dynamically turn off and turn on the
networks of high-speed clocks.
This is done tracking the routes to the sinks and if the route passes
through a special HCLK MUX (this may be the input MUX or the output MUX,
as well as the interbank MUX), then the control signal of this MUX is
used.
Signed-off-by: YRabbit <rabbit@yrabbit.cyou>