perf: fix buildpaths QA warning

perf: fix buildpaths QA warning

In the 6.2+ kernel, arm64 perf has a buildpaths QA warning as
a syscall table is now being dynamically generated. That generated
table includes unistd.h by absolute path, which in turn triggers
the buildpaths QA warning.

This could easily be patched in linux-yocto, but that would
leave the QA issue in perf built from other kernel trees.

So we instead to the following:

 - Add the perf tools directory to the include path
 - Modify the Makefile to have a relative path to unistd.h and
   pass both the relative and absolute path to the generation
   script
 - Modify the generation script to take the relative location
   of unistd.h as a new parameter, and use that in the generated
   sycalls.c file

At build, the added include path of the perf source allows the
relative path file to be included, and no buildpaths warning is
generated.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>