cavs: disable all interrupts when configuring interrupt controllers

Some interrupts can be enabled by the ROM, e.g. the timer interrupt.
When then in Zephyr the interrupt controller is enabled, before
individual interrupts are configured, interrupts can arrive and lead
to the spurious interrupt handler being invoked. Fix thid by
disabling all child interrupts when configuring cAVS interrupt
controllers.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>