remoteproc: imx_rproc: Add IMX_RPROC_SCU_API method

On i.MX8QM and i.MX8QXP, most devices are controlled
by System Control Unit, so add IMX_RPROC_SCU_API
method for these platform.
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1633944015-789-3-git-send-email-shengjiu.wang@nxp.comSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

drivers/remoteproc/imx_rproc.h

@@ -22,6 +22,8 @@ enum imx_rproc_method {
 	IMX_RPROC_MMIO,
 	/* Through ARM SMCCC */
 	IMX_RPROC_SMC,
+	/* Through System Control Unit API */
+	IMX_RPROC_SCU_API,
 };
 
 struct imx_rproc_dcfg {