drm/amdgpu: check entity lock is held in amdgpu_ttm_job_submit

drm/amdgpu: check entity lock is held in amdgpu_ttm_job_submit

drm_sched_job_arm and drm_sched_entity_push_job must be called
under the same lock to guarantee the order of execution.

This commit adds a check in amdgpu_ttm_job_submit and fix the
places where the lock was missing.

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>