muen-timer: Initialize clock event driver earlier

This makes the clock event device available during module
initialization, e.h. Intel's e1000e driver.
muen-timer: Initial clock event using timer page

Use Muen subject timer page to set next event. Only one-shot mode is
supported. Currently the address of the timer page is hard-coded to
0xe00000000 for now.
muen-timer: Warn when setting unsupported mode
muen-timer: Raise priority of muen-timer clock event driver

Make sure that Muen Timer is used as clock event device, if present.
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.