ipc: intel_adsp: Ensure IPC completion before runtime idle

Prevent the system from entering runtime idle state during IPC
transactions until the HOST acknowledgment is received.

This patch modifies the IPC mechanism to:
- Lock the runtime idle state immediately after sending an IPC message
  to the HOST, preventing the system from entering a low-power state.
- Unlock the runtime idle state once the IPC transaction is acknowledged
  by the HOST, allowing the system to enter low-power states if
  conditions permit.

The changes ensure that the DSP does not enter a power state that could
interrupt the IPC communication process, maintaining the integrity of
the IPC state machine.

Signed-off-by: Tomasz Leman <tomasz.m.leman@intel.com>