memory: mtk-smi: Add PM suspend and resume ops

In the commit 4f0a1a1a ("memory: mtk-smi: Invoke pm runtime_callback
to enable clocks"), we use pm_runtime callback to enable/disable the smi
larb clocks. It will cause the larb's clock may not be disabled when
suspend. That is because device_prepare will call pm_runtime_get_noresume
which will keep the larb's PM runtime status still is active when suspend,
then it won't enter our pm_runtime suspend callback to disable the
corresponding clocks.

This patch adds suspend pm_ops to force disable the clocks, Use "LATE" to
make sure it disable the larb's clocks after the multimedia devices.

Fixes: 4f0a1a1a ("memory: mtk-smi: Invoke pm runtime_callback to enable clocks")
Signed-off-by: Anan Sun <anan.sun@mediatek.com>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>