power/reset: Make the vexpress driver optional on arm and arm64

The driver can be used on either arm or arm64 platforms, but
the latter doesn't have any platform-specific configuration
options, so it must be possible to manually enable the driver.
Signed-off-by: NPawel Moll <pawel.moll@arm.com>
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NAnton Vorontsov <anton@enomsg.org>

drivers/power/reset/Kconfig

@@ -32,7 +32,8 @@ config POWER_RESET_RESTART
 	  user presses a key. u-boot then boots into Linux.
 
 config POWER_RESET_VEXPRESS
-	bool
+	bool "ARM Versatile Express power-off and reset driver"
+	depends on ARM || ARM64
 	depends on POWER_RESET
 	help
 	  Power off and reset support for the ARM Ltd. Versatile