mailbox: mtk-cmdq: add gce ddr enable support flow

add gce ddr enable control flow when gce suspend/resume

when all cmdq instruction task has been processed done,
we need set this gce ddr enable to disable status to tell
cmdq hardware gce there is none task need process, and the hardware
can go into idle mode and no access ddr anymore, then the spm can go
into suspend.

the original issue is gce still access ddr when cmdq suspend function
call, but there is no task run.
so, we need control gce access ddr with this flow.
when cmdq suspend function, there is no task need process, we can
disable gce access ddr, to make sure system go into suspend success.

Signed-off-by: Yongqiang Niu <yongqiang.niu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>