remoteproc: imx_dsp_rproc: Wait for suspend ACK only if WAIT_FW_CONFIRMATION is set

remoteproc: imx_dsp_rproc: Wait for suspend ACK only if WAIT_FW_CONFIRMATION is set

The DSP suspend path currently waits unconditionally for a suspend ack
from the firmware. This breaks firmwares that do not implement the
mailbox-based CONFIRMATION handshake, as the DSP never responds and
system suspend fails with -EBUSY.

The driver already uses the WAIT_FW_CONFIRMATION flag to indicate that
the firmware supports the CONFIRMATION handshake at boot. Apply the same
logic during suspend: only send the suspend message and wait for the
suspend ack when the firmware is expected to support it.

Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20251204122825.756106-3-iuliana.prodan@oss.nxp.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>