muen-timer: Register TSC tickrate as clockevent freq

Use the muen_get_tsc_khz() function to retrieve the host's TSC frequency
and register it as the clockevent frequency.
muen-timer: Declare UINT_MAX as max_delta_ticks

The value argument on the timer page is uint64_t and designates an
absolute time in ticks. Therefore allow UINT_MAX as maximum relative
time in ticks.
muen-timer: Use rdtsc to set timer page value

Set the absolute time in ticks the next event is supposed to fire by
adding the current TSC value to the delta.