clocksource/cadence_ttc: Remove clocksource clock notifier

clocksource/cadence_ttc: Remove clocksource clock notifier

The clocksource's clock notifier tried to keep the clocksource frequency
adjusted when the input clock changed. The approach included rather
heavy operations and results in a deadlock on current kernels (the
clocksource is unregistered and re-registered with the new frequency).
Removing the notifier keeps the system operational on cost of timing
being off.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>