xen/arm: XEN selects ARM_PSCI

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

arch/arm/Kconfig

@@ -1892,6 +1892,7 @@ config XEN
 	depends on ARM && AEABI && OF
 	depends on CPU_V7 && !CPU_V6
 	depends on !GENERIC_ATOMIC64
+	select ARM_PSCI
 	help
 	  Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.