x86/tsc: Finalize the split of the TSC_RELIABLE flag

All places which used the TSC_RELIABLE to skip the delayed calibration
have been converted to use the TSC_KNOWN_FREQ flag.

Make the immeditate clocksource registration, which skips the long term
calibration, solely depend on TSC_KNOWN_FREQ.

The TSC_RELIABLE now merily removes the requirement for a watchdog
clocksource.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Bin Gao <bin.gao@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>