remoteproc: imx_dsp_rproc: Use devm_pm_runtime_enable() helper

remoteproc: imx_dsp_rproc: Use devm_pm_runtime_enable() helper

Current code on the cleanup path just disables runtime PM for a device.

Using resource managed version devm_pm_runtime_enable() registers a cleanup
callback that sets autosuspend to false and then disables runtime PM for
a device. So, basically the same functionality as we don't use autosuspend
anyway.

As a result, the .remove callback is no longer needed, reducing boilerplate
code.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Reviewed-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Tested-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20251119-imx-dsp-2025-11-19-v4-3-adafd342d07b@nxp.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>