drivers: i2s_mcux_sai: control MCLK direction with DT property

For the SAI peripheral, the MCLK signal input/output direction is
independent from the TX or RX bit clocks directions (TCR2[BCD] and
RCR2[BCD]). Introduces mclk-output property.

Signed-off-by: Derek Snell <derek.snell@nxp.com>