remoteproc: imx_dsp_rproc: Document run_stall struct member

Add documentation for 'run_stall' imx_dsp_rproc struct member.
This also fixes the following warning:

warning: Function parameter or struct member 'run_stall'
not described in 'imx_dsp_rproc'

Fixes: 0184b4f ("imx_dsp_rproc: Use reset controller API to control the DSP")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202503142125.IE33sCto-lkp@intel.com/
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20250314151720.1793719-1-daniel.baluta@nxp.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

Author: dbaluta

drivers/remoteproc/imx_dsp_rproc.c

@@ -96,6 +96,7 @@ enum imx_dsp_rp_mbox_messages {
 /**
  * struct imx_dsp_rproc - DSP remote processor state
  * @regmap: regmap handler
+ * @run_stall: reset control handle used for Run/Stall operation
  * @rproc: rproc handler
  * @dsp_dcfg: device configuration pointer
  * @clks: clocks needed by this device