On the documentation of the sample "perf" the path for the script
"stackcollapse" is incorrect.
Fix the path
Signed-off-by: Miguel Gazquez <miguel.gazquez@bootlin.com>
Clean up documentation pages for the new perf tool
as they contained several typos, grammar errors, and
duplicated content between main doc page and sample
page
Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>