drivers: dai: sai: disable IRQs when not needed

IRQs are currently only enabled during the driver
initialization function (i.e: sai_init()). As such,
even though they're not needed (i.e: after a TRIGGER_STOP
operation) they remain enabled. Fix this by enabling IRQs
after during the TRIGGER_START operation and disabling them
during the TRIGGER_STOP operation.

This change is required by irq chips (i.e: irqsteer) which
perform PM operations during irq_enable()/irq_disable(). If
interrupts are left enabled all the time that means the irq
chip's PM resources might also remain enabled.

To make this change possible, the irq will have to be stored
inside the SAI's configuration structure.

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