drm/scheduler: improve job distribution with multiple queues

This patch uses score based logic to select a new rq for better
loadbalance between multiple rq/scheds instead of num_jobs.

Below are test results after running amdgpu_test from mesa drm

Before this patch:

sched_name     num of many times it got scheduled
=========      ==================================
sdma0          314
sdma1          32
comp_1.0.0     56
comp_1.0.1     0
comp_1.1.0     0
comp_1.1.1     0
comp_1.2.0     0
comp_1.2.1     0
comp_1.3.0     0
comp_1.3.1     0
After this patch:

sched_name     num of many times it got scheduled
=========      ==================================
sdma0          216
sdma1          185
comp_1.0.0     39
comp_1.0.1     9
comp_1.1.0     12
comp_1.1.1     0
comp_1.2.0     12
comp_1.2.1     0
comp_1.3.0     12
comp_1.3.1     0

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>