drm/amdgpu:add hang_limit for sched(v2)

since gpu_scheduler source domain cannot access amdgpu variable
so need create the hang_limit membewr for sched, and it can
refer it for the upcoming GPU RESET patches

v2:
make hang_limit a parameter of sched_init()

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Chunming Zhou <David1.Zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>