drm/i915/selftests: Live tests emit requests and so require rpm

As we emit requests or touch HW directly for some of the live tests, the
requirement is that we hold the rpm wakeref before doing so. We want a
mix of granularity since we will want to test runtime suspend, so try to
mark up only the critical sections where we need rpm for the live test.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108002
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180920144934.16611-1-chris@chris-wilson.co.uk