The current driver support stop mode by calling machine api.
The patch add dts support to set GPR register for stop request.

imx8mq enter stop/exit stop mode by setting GPR bit, which can
be accessed by A core.
imx8qm enter stop/exit stop mode by calling IMX_SC ipc APIs that
communicate with M core ipc service, and the M core set the related
GPR bit at last.
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>