drm/i915/perf: ensure selftests select valid format

Gen12 only support a single report format :
I915_OA_FORMAT_A32u40_A4u32_B8_C8

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 00a7f0d7

 ("drm/i915/tgl: Add perf support on TGL")
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191029142826.20014-1-lionel.g.landwerlin@intel.com