drm/amdgpu: Allocate coredump ring buffers per ring

drm/amdgpu: Allocate coredump ring buffers per ring

Allocate each ring buffer separately. A single allocation summing all
ring sizes can exceed the page allocator's MAX_ORDER limit and fail;
per-ring buffers stay small enough to satisfy. The existing allocation
style doesn't capture any ring data if the huge allocation fails.
Splitting into multiple allocations helps to capture as much data as
possible for the core dump.

A failed ring is left with a NULL buffer and skipped when formatting.

Fixes: eea85914d15b ("drm/amdgpu: save ring content before resetting the device")
Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Assisted-by: Claude Code
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 3e8e92b7892a6377bef86106bfff1b98cf586aee)
Cc: stable@vger.kernel.org