KVM: Give IRQFD its own separate enabling Kconfig option

Currently, the IRQFD code is conditional on CONFIG_HAVE_KVM_IRQ_ROUTING.
So that we can have the IRQFD code compiled in without having the
IRQ routing code, this creates a new CONFIG_HAVE_KVM_IRQFD, makes
the IRQFD code conditional on it instead of CONFIG_HAVE_KVM_IRQ_ROUTING,
and makes all the platforms that currently select HAVE_KVM_IRQ_ROUTING
also select HAVE_KVM_IRQFD.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Tested-by: Eric Auger <eric.auger@linaro.org>
Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/s390/kvm/Kconfig

@@ -26,6 +26,7 @@ config KVM
 	select KVM_ASYNC_PF
 	select KVM_ASYNC_PF_SYNC
 	select HAVE_KVM_IRQCHIP
+	select HAVE_KVM_IRQFD
 	select HAVE_KVM_IRQ_ROUTING
 	---help---
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