Add mailbox controller driver for CV18XX SoCs, which provides 8 channels
and each channel has an 8-byte FIFO.
Signed-off-by: Yuntao Dai <d1581209858@live.com>
Signed-off-by: Junhui Liu <junhui.liu@pigmoral.tech>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
