A bunch of tests for the new i915 PMU feature.

Parts of the code were initialy sketched by Dmitry Rogozhkin.

v2: (Most suggestions by Chris Wilson)
 * Add new class/instance based engine list.
 * Add gem_has_engine/gem_require_engine to work with class/instance.
 * Use the above two throughout the test.
 * Shorten tests to 100ms busy batches, seems enough.
 * Add queued counter sanity checks.
 * Use igt_nsec_elapsed.
 * Skip on perf -ENODEV in some tests instead of embedding knowledge locally.
 * Fix multi ordering for busy accounting.
 * Use new guranteed_usleep when sleep time is asserted on.
 * Check for no queued when idle/busy.
 * Add queued counter init test.
 * Add queued tests.
 * Consolidate and increase multiple busy engines tests to most-busy and
   all-busy tests.
 * Guarantte interrupts by using fences.
 * Test RC6 via forcewake.

v3:
 * Tweak assert in interrupts subtest.
 * Sprinkle of comments.
 * Fix multi-client test which got broken in v2.

v4:
 * Measured instead of guaranteed sleep.
 * Missing sync in no_sema.
 * Log busyness before asserts for debug.
 * access(2) instead of open(2) to determine if cpu0 is hotpluggable.
 * Test frequency reporting via min/max setting instead assuming.
   ^^ All above suggested by Chris Wilson. ^^
 * Drop queued subtests to match i915.
 * Use long batches with fences to ensure interrupts.
 * Test render node as well.

v5:
 * Add to meson build. (Petri Latvala)
 * Use 1eN constants. (Chris Wilson)
 * Add tests for semaphore and event waiting.

v6:
 * Fix interrupts subtest by polling the fence from the "outside".
   (Chris Wilson)

v7:
 * Assert number of initialized engines matches the expectation.
   (Chris Wilson)
 * Warn instead of skipping if we couldn't restore the initial
   frequency. (Chris Wilson)
 * Move all asserts to after the test cleanup (just a tidy).
 * More 1eN notation for timeouts.
 * Bump the tolerance to 5% since I saw a few noisy runs with
   sampling counters.
 * Always start the PMU before submitting batches to lower
   reliance on i915 doing the delayed engine busy stats disable.

v8:
 * Update for upstream engine class enum.

v9:
 * Add meson build support.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>