arm64: dts: imx8mp: Add analog audio output on i.MX8MP EVK

Enable SAI3 on i.MX8MP EVK, add WM8960 codec binding and regulator.
This is all that is needed to get analog audio output operational
on i.MX8MP EVK.

Acked-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>