[streamers] bugfix of streamers simulation

For simulation, the second duration is forced to be shorter with the
generic g_sim_cycle_counter_range. The problem is that the tai/cycle
counters are still counting full seconds, the trick was done only
when calculating the delay in function f_cycles_counter_range()
in fixed_latency_ts_match.vhd. This worked fine unless the timestamps
were at the edge of the "shorter" second and fixed-latency was
enabled. In such case, it happened that the time of releasing
data from streamers was calcualted for TAI+1, yet TAI was incremented
after the "true" second, not the shorter one. So, the simulation
was stuck.

To avoid messing up with PPS gen in which the tai/cycles are
generated, for simulation the tai/cycle values are overriden
in the xwr_streamer top module. This "alternative" TAI time
is counted from the time when time_valid goes HIGH.

This solution should work for streamers, provided that tx/rx
instances have the time_valid go HIGH more or less at the same time.
As far as I can tell, this is usually the case.