wb_intercon: allow single master/slaves

The result of clog2(1) = 0, which will result in
master/slave_sel bit vectors of [-1:0].
Threat the special case of num_masters/slaves == 1,
so a bit vector [0:0] is created.
wb_intercon: fix multiple masters to single slave connections

The commit: 5f7cbf7e77a6d54641efc4c832628265a605d1e2
'wb_intercon: fix single slave connections'
took care of the case with a single master connected to
a single slave. The case with several masters connected
to a single slave was however oversighted.
cores/mor1kx: add mor1kx_monitor

This enables the use of mor1kx_monitor and the associated
plusargs.
systems: add mor1kx-generic

Heavily based on the or1200-generic system, the mor1kx-generic
system serves the same kind of purpose - to provide a minimal
simulation platform, but for mor1kx instead of or1200.
verilator_tb_utils: change all 'times' to uint64_t

Franck Jullien reported that unsigned long is not a valid argument
for tfp->dump() on 32-bit machines.
This changes all 'time' (cycles, really) references to uint64_t.