firmware: mediatek: Add adsp ipc protocol interface

firmware: mediatek: Add adsp ipc protocol interface

Some of mediatek processors contain
the Tensilica HiFix DSP for audio processing.

The communication between Host CPU and DSP firmware is
taking place using a shared memory area for message passing.

ADSP IPC protocol offers (send/recv) interfaces using
mediatek-mailbox APIs.

We use two mbox channels to implement a request-reply protocol.

Signed-off-by: Allen-KH Cheng <[email protected]>
Signed-off-by: TingHan Shen <[email protected]>
Reviewed-by: Pierre-Louis Bossart <[email protected]>
Reviewed-by: Curtis Malainey <[email protected]>
Reviewed-by: Tzung-Bi Shih <[email protected]>
Reviewed-by: YC Hung <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mark Brown <[email protected]>