drm/amdgpu: Increase soft IH ring size

Retry faults are delegated to soft IH ring and then processed by
deferred worker. Current soft IH ring size PAGE_SIZE can store 128
entries, which may overflow and drop retry faults, causes HW stucks
because the retry fault is not recovered.

Increase soft IH ring size to 8KB, enough to store 256 CAM entries
because we clear the CAM entry after handling the retry fault from soft
ring.

Define macro IH_RING_SIZE and IH_SW_RING_SIZE to remove duplicate
constant.

Show warning message if soft IH ring overflows with CAM enabled because
this should not happen.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>