remoteproc: imx_dsp_rproc: mark PM functions as __maybe_unused

remoteproc: imx_dsp_rproc: mark PM functions as __maybe_unused

When CONFIG_PM_SLEEP is disabled, we get a harmless warning:

drivers/remoteproc/imx_dsp_rproc.c:1145:12: error: 'imx_dsp_resume' defined but not used [-Werror=unused-function]
 1145 | static int imx_dsp_resume(struct device *dev)
      |            ^~~~~~~~~~~~~~
drivers/remoteproc/imx_dsp_rproc.c:1110:12: error: 'imx_dsp_suspend' defined but not used [-Werror=unused-function]
 1110 | static int imx_dsp_suspend(struct device *dev)
      |            ^~~~~~~~~~~~~~~

Mark these as __maybe_unused to get a clean build.

Fixes: ec0e5549f358 ("remoteproc: imx_dsp_rproc: Add remoteproc driver for DSP on i.MX")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20211014075239.3714694-1-arnd@kernel.org
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>