i915/i915_selftests: Expose 'perf' selftests

Find all the perf* selftests and expose them in our igt. In CI we expect
these not to be run in BAT (since they are just performance tests rather
than conformance), but expect the results to be available from the
shards.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

tests/i915/i915_selftest.c

@@ -40,4 +40,9 @@ igt_main
 			    "live_selftests=-1 disable_display=1 st_filter=%s",
 			    env) < sizeof(opts));
 	igt_kselftests("i915", opts, "live_selftests", "live");
+
+	igt_assert(snprintf(opts, sizeof(opts),
+			    "perf_selftests=-1 disable_display=1 st_filter=%s",
+			    env) < sizeof(opts));
+	igt_kselftests("i915", opts, "perf_selftests", "perf");
 }