drm/amdgpu: Log the creation of a coredump file

After a GPU reset happens, the driver creates a coredump file. However,
the user might not be aware of it. Log the file creation the user can
find more information about the device and add the file to bug reports.
This is similar to what the xe driver does.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>