linux-imx

MLK-19042-1: ASoC: fsl_rpmsg_i2s: support low power audio

Add two new message command I2S_TX_POINTER and I2S_RX_POINTER,
which are used to get the hw pointer in m4 side. For in low
power audio mode, m4 won't send notification every period, the
notification only be sent when hw pointer reach end of buffer,
so we need these command to get the position of hw pointer,
user can use it to calculate the timestamp.

Restructure send message and recv message together for i2s_rpmsg,
that every send message has a recv message. so the
i2s_send_message can store the recv message indepedently. one
reason is that the receive message is async withe send message.

The low power audio is disabled in default, user need to enabled
it by add "fsl,enable-lpa" in dts.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Reviewed-by: Viorel Suman <viorel.suman@nxp.com>
(cherry picked from commit 753e7b819609ad4791e32069a124d4411c720947)