drm/amdgpu: disable gpu-sched load balance for uvd

On hardware with multiple uvd instances, dependent uvd jobs
may get scheduled to different uvd instances. Because uvd_enc
jobs retain hw context, dependent jobs should always run on the
same uvd instance. This patch disables GPU scheduler's load balancer
for a context that binds jobs from the same context to a uvd
instance.

v2: Squash in uvd_enc fix

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