Add SNVS power off support. The SNVS_LP LPCR register could
drive signal to PMIC to turn off system power.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20230323123907.103719-1-peng.fan@oss.nxp.com


Signed-off-by: Rob Herring <robh@kernel.org>