drm/sched: Add some more scheduling quality unit tests

drm/sched: Add some more scheduling quality unit tests

This time round we explore the rate of submitted job queue processing
with multiple identical parallel clients.

Example test output:

3 clients:
        t               cycle:     min  avg max : ...
        +     0ms                   0    0    0 :   0   0   0
        +   102ms                   2    2    2 :   2   2   2
        +   208ms                   5    6    6 :   6   5   5
        +   310ms                   8    9    9 :   9   9   8
...
        +  2616ms                  82   83   83 :  83  83  82
        +  2717ms                  83   83   83 :  83  83  83
    avg_max_min_delta(x100)=60

Every 100ms for the duration of the test it logs how many jobs each
client had completed, prefixed by minimum, average and maximum numbers.
When finished overall average delta between max and min is output as a
rough indicator to scheduling fairness.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Philipp Stanner <phasta@kernel.org>
Cc: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Tested-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patch.msgid.link/20260417103744.76020-6-tvrtko.ursulin@igalia.com