CI doesn't run in whole-test mode, but runs each subtest individually.
Tests that are designed to do a block of work to be shared between many
subtests end up running that work multiple times (once per subtest) and
worse, that work is wasted if the subtest will be skipped.

pm_rc6_residency is one such example that measured all the residencies
up front before skipping, each skip was therefore taking in excess of
10s.

v2: Put a small delay back before starting measurements as rc6 doesn't
start until an evaluation interval after idling.
v3: Drop rc6p+ tests; we have no control over the hw whether it decides
to use rc6 or deeper (we can enable it, but not dictate it).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ewelina Musial <ewelina.musial@intel.com> #v1