top: tweak hotplugged response and frame refresh logic

top: tweak hotplugged response and frame refresh logic

For some time now, top has refrained from updating the
current number of cpus and memory totals with each and
every refresh cycle. Rather, to lessen overhead costs,
such values are updated periodically (5 min & 3 secs).

The delay in updating the cpu count was only important
with the addition of a cpu, since any loss is detected
immediately. And the large interval was chosen because
of the costs once associated with a glibc sysconf call
and an unlikely scenario of physically adding the cpu.

But the ease with which cpus can be taken offline then
placed back online under linux suggests that 5 minutes
may be too high. So, without addressing the likelihood
of that act, top is now more responsive in these ways:

1) that 5 minute interval has been reduced to 1 minute
2) any key, not just Enter/Space, refreshes cpus & mem

Note: we leave the man document as is, suggesting that
only the Enter/Space keys force an update for hotplug.

Signed-off-by: Jim Warner <james.warner@comcast.net>