drm/amdgpu/gmc8: Delegate VM faults to soft IRQ handler ring

drm/amdgpu/gmc8: Delegate VM faults to soft IRQ handler ring

On old GPUs, it may be an issue that handling the interrupts from
VM faults is too slow and the interrupt handler (IH) ring may
overflow, which can cause an eventual hang.

Delegate the processing of all VM faults to the soft
IRQ handler ring.

As a result, we spend much less time in the IRQ handler that
interacts with the HW IH ring, which significantly reduces the
chance of hangs/reboots.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>