drivers: dai: sai: use "dmas" property for handshake encoding

Since a DMA cell now allows specifying a channel and a MUX value
there's no need to fetch these values from the HAL. This, in turn,
allows for more flexibility and reduces the coding effort for new
platforms that want to use the SAI driver.

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>