perf, sched migration: Parameterize cpu height and spacing

Without vertical zoom, it is not possible to see all CPUs in a trace
taken on a larger machine. This patch parameterizes the height and
spacing of CPUs so that you can fit more cpus into the screen.

Ideally we should dynamically size/space the CPU rectangles with some
minimum threshold. Until then, this patch is a stop-gap.

Signed-off-by: Nikhil Rao <ncrao@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>