mailbox: mtk-cmdq: Add cmdq private data to cmdq_pkt for generating instruction

mailbox: mtk-cmdq: Add cmdq private data to cmdq_pkt for generating instruction

Add the cmdq_mbox_priv structure to store the private data of GCE,
such as the shift bits of the physical address. Then, include the
cmdq_mbox_priv structure within the cmdq_pkt structure.

This allows CMDQ users to utilize the private data in cmdq_pkt to
generate GCE instructions when needed. Additionally, having
cmdq_mbox_priv makes it easier to expand and reference other GCE
private data in the future.

Add cmdq_get_mbox_priv() for CMDQ users to get all the private data
into the cmdq_mbox_priv of the cmdq_pkt.

Signed-off-by: Jason-JH Lin <jason-jh.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>