drm/amdgpu: Introduce cached_rptr and is_guilty callback in amdgpu_ring

This patch introduces the following changes:
- Add `cached_rptr` to the `amdgpu_ring` structure to store the read pointer before a reset.
- Add `is_guilty` callback to the `amdgpu_ring_funcs` structure to check if a ring is guilty of causing a timeout.

Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>