perf test: Extend branch stack sampling test for Arm64 BRBE

Add Arm64 BRBE-specific testing to the existing branch stack sampling
test.

The test currently passes on the FVP RevC model [1], but no hardware has
been tested yet.

[1]: https://developer.arm.com/Tools%20and%20Software/Fixed%20Virtual%20Platforms



Co-authored-by: German Gomez <german.gomez@arm.com>
Signed-off-by: James Clark <james.clark@arm.com>