selftests/amd-pstate: Added option to provide perf binary path

In selftests/amd-pstate, distro `perf` is used to capture `perf stat`
while running microbenchmarks. Distro `perf` is not working with
upstream kernel. Fix this by providing an option to give the perf
binary path.

Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>