powerpc/kvm: Fix ppc64_defconfig + PPC_POWERNV=n build error

kvm_no_guest() calls power7_wakeup_loss() to put the thread into the
deepest supported idle state. power7_wakeup_loss() is defined in
arch/powerpc/kernel/idle_power7.S, which is compiled only when
PPC_P7_NAP=y.

And PPC_P7_NAP is selected when PPC_POWERNV=y.

Hence in cases where PPC_POWERNV=n and KVM_BOOK3S_64_HV=y we see the
following error:

  arch/powerpc/kvm/built-in.o: In function `kvm_no_guest':
  arch/powerpc/kvm/book3s_hv_rmhandlers.o:(.text+0x42c): undefined reference to `power7_wakeup_loss'

Fix this by adding PPC_POWERNV as a dependency for KVM_BOOK3S_64_HV.
Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/Kconfig

@@ -75,7 +75,7 @@ config KVM_BOOK3S_64
 
 config KVM_BOOK3S_64_HV
 	tristate "KVM support for POWER7 and PPC970 using hypervisor mode in host"
-	depends on KVM_BOOK3S_64
+	depends on KVM_BOOK3S_64 && PPC_POWERNV
 	select KVM_BOOK3S_HV_POSSIBLE
 	select MMU_NOTIFIER
 	select CMA