KVM: PPC: Move kvmhv_on_pseries() into kvm_ppc.h

We recently introduced a usage of kvmhv_on_pseries() in powerpc.c, which
causes a build error for ppc64_book3e_allmodconfig:

  arch/powerpc/kvm/powerpc.c:716:8: error: implicit declaration of function ‘kvmhv_on_pseries’
    716 |    if (kvmhv_on_pseries()) {
        |        ^~~~~~~~~~~~~~~~

Fix it by moving kvmhv_on_pseries() into kvm_ppc.h so that the stub
version is available for book3e builds.

Fixes: f771b55 ("KVM: PPC: Use KVM_CAP_PPC_AIL_MODE_3")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/kvm_book3s_64.h

@@ -16,18 +16,6 @@
 #include <asm/ppc-opcode.h>
 #include <asm/pte-walk.h>
 
-#ifdef CONFIG_PPC_PSERIES
-static inline bool kvmhv_on_pseries(void)
-{
-	return !cpu_has_feature(CPU_FTR_HVMODE);
-}
-#else
-static inline bool kvmhv_on_pseries(void)
-{
-	return false;
-}
-#endif
-
 /*
  * Structure for a nested guest, that is, for a guest that is managed by
  * one of our guests.

arch/powerpc/include/asm/kvm_ppc.h

@@ -586,6 +586,18 @@ static inline bool kvm_hv_mode_active(void)		{ return false; }
 
 #endif
 
+#ifdef CONFIG_PPC_PSERIES
+static inline bool kvmhv_on_pseries(void)
+{
+	return !cpu_has_feature(CPU_FTR_HVMODE);
+}
+#else
+static inline bool kvmhv_on_pseries(void)
+{
+	return false;
+}
+#endif
+
 #ifdef CONFIG_KVM_XICS
 static inline int kvmppc_xics_enabled(struct kvm_vcpu *vcpu)
 {