drivers: firmware: psci: Register with kernel restart handler

Register with kernel restart handler instead of setting arm_pm_restart
directly. This enables support for replacing the PSCI restart handler
with a different handler if necessary for a specific board.

Select a priority of 129 to indicate a higher than default priority, but
keep it as low as possible since PSCI reset is known to fail on some
boards.

Change-Id: I74d824186de527bde39b1e8a3d96351261e73a60
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Stefan Agner <stefan.agner@toradex.com>
Patch-mainline: https://lore.kernel.org/patchwork/patch/1139628/


Signed-off-by: Elliot Berman <eberman@codeaurora.org>