dim: add new interfaces for initialization and getting results

DIM-related mode and work have been collected in one same place,
so new interfaces are added to provide convenience.

Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240621101353.107425-5-hengqi@linux.alibaba.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>