[S390] cleanup s390 Kconfig

Make use of def_bool and def_tristate where possible and add sensible
defaults to the config symbols where applicable. This shortens the
defconfig file by another ~40 lines.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index a725158..f66a1bd 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -4,8 +4,8 @@
 source "virt/kvm/Kconfig"
 
 menuconfig VIRTUALIZATION
-	bool "Virtualization"
-	default y
+	def_bool y
+	prompt "Virtualization"
 	---help---
 	  Say Y here to get to see options for using your Linux host to run other
 	  operating systems inside virtual machines (guests).
@@ -16,7 +16,8 @@
 if VIRTUALIZATION
 
 config KVM
-	tristate "Kernel-based Virtual Machine (KVM) support"
+	def_tristate y
+	prompt "Kernel-based Virtual Machine (KVM) support"
 	depends on HAVE_KVM && EXPERIMENTAL
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES