[S390] Kconfig: refine depends statements.

Refine some depends statements to limit their visibility to the
environments that are actually supported.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/kvm/Kconfig b/drivers/kvm/Kconfig
index 703cc88..e8e37d8 100644
--- a/drivers/kvm/Kconfig
+++ b/drivers/kvm/Kconfig
@@ -2,6 +2,7 @@
 # KVM configuration
 #
 menu "Virtualization"
+	depends on X86
 
 config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support"