trace-cmd: Do not free pages from the lookup table in struct cpu_data in case trace file is loaded.

A major speed regression in trace-cmd v2.8 is reported by Johannes Berg
when parsing a huge trace.dat file:

"I have a ~1.7G file with just under 620k events (not exactly big by our standards),
and parsing speed (with -N to disable plugins) goes from ~4.5 seconds on commit
1ad32c24746 to >>4.5 minutes (I aborted there) on master.
I was talking to Steven about another issue, and he pointed me to
commit c2fc2bc296f7. Reverting that on master makes it take ~2 seconds,
so that'd actually be an improvement."

Proposed solution: do not free pages from "struct page **pages" lookup table
in struct cpu_data, in case a trace file is loaded. This reverts the behavior
for this use case, as it was before commit c2fc2bc296f7.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203411
Link: http://lore.kernel.org/linux-trace-devel/20190619114922.3169-1-tz.stoyanov@gmail.com

Fixes: c2fc2bc296f7 ("trace-cmd: Fix crash when trace-cmd is executed with args profile -F sleep 1")
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Tested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>