How to get audio through the low speed header in hikey?

Hi,

I am trying to enable the i2s audio on the hikey and I am trying to use the low speed header for the connection between the hikey and audio codec.

How can I enable the low speed header to send the i2s data on it?
I am using the pins:
MODEM_PCM_XFS
MODEM_PCM_XCLK
MODEM_PCM_DO
MODEM_PCM_DI

Can somebody help me please?