perf evlist: Always do automatic allocation of pollfd and mmap structures

perf evlist: Always do automatic allocation of pollfd and mmap structures

At first tools were required to do that, but while writing the python
bindings to simplify the API I made them auto-allocate when needed.

This just makes record, stat and top use that auto allocation,
simplifying them a bit.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-iokhcvkzzijr3keioubx8hlq@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>