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.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>