power: reset: driver for the Versatile syscon reboot

This driver enabled us to drive the reboot of the Versatile family
of ARM reference boards. Even though only the RealView boards are
supported initially, these boards all have the same procedure for
reboot:

- Write a magic value into an unlocking register
- Write another magic value into a reset control register

The driver will be reusable for Versatile and possibly also the
Integrator family of reference boards.

Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Acked-By: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/power/reset/Kconfig

@@ -92,6 +92,15 @@ config POWER_RESET_SUN6I
 	help
 	  Reboot support for the Allwinner A31 SoCs.
 
+config POWER_RESET_VERSATILE
+	bool "ARM Versatile family reboot driver"
+	depends on ARM
+	depends on MFD_SYSCON
+	depends on OF
+	help
+	  Power off and restart support for ARM Versatile family of
+	  reference boards.
+
 config POWER_RESET_VEXPRESS
 	bool "ARM Versatile Express power-off and reset driver"
 	depends on ARM || ARM64