imx: imx9: Add MIX power init

Add power init of MEDIAMIX, MLMIX and DDRMIX. And clear isolation
of MIPI DSI/CSI, USBPHY after the power up.

SPL should call the power init in its boot sequence before accessing
above three MIX and USB.

Signed-off-by: Peng Fan <peng.fan@nxp.com>