perf tools: Fix spelling mistakes

Mostly in the documentation.

Signed-off-by: Kim Phillips <kim.phillips@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170503131350.cebeecd8bd0f2968417626ab@arm.com


[ Fix spelling of "parameter" in one of the spell-checked lines ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>