memory: mtk-smi: Get rid of need_larbid

The "mediatek,larb-id" has already been parsed in MTK IOMMU driver.
It's no need to parse it again in SMI driver. Only clean some codes.
This patch is fit for all the current mt2701, mt2712, mt7623, mt8173
and mt8183.

After this patch, the "mediatek,larb-id" only be needed for mt2712
which have 2 M4Us. In the other SoCs, we can get the larb-id from M4U
in which the larbs in the "mediatek,larbs" always are ordered.

Correspondingly, the larb_nr in the "struct mtk_smi_iommu" could also
be deleted.

CC: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>