perf session: Use sensible mmap size

On 64bit we can map the whole file in one go, on 32bit we can at least map
32MB and not map/unmap tiny chunks of the file.

Base the progress bar on 1/16 of the data size.

Preparatory patch to get rid of the malloc/memcpy/free of trace data.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20101130163820.213687773@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>