qemu: Add conditions for qemu-kvm use on ppc64

qemu-kvm can be used to run ppc64 guests on ppc64le hosts and vice
versa, since the hardware is actually the same and the endianness
is chosen by the guest kernel.

Up until now, however, libvirt didn't allow the use of qemu-kvm
to run guests if their endianness didn't match the host's.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1267882
(cherry picked from commit 938368f8)

src/qemu/qemu_capabilities.c

@@ -741,7 +741,7 @@ virQEMUCapsInitGuest(virCapsPtr caps,
     char *binary = NULL;
     virQEMUCapsPtr qemubinCaps = NULL;
     virQEMUCapsPtr kvmbinCaps = NULL;
-    bool native_kvm, x86_32on64_kvm, arm_32on64_kvm;
+    bool native_kvm, x86_32on64_kvm, arm_32on64_kvm, ppc64_kvm;
     int ret = -1;
 
     /* Check for existence of base emulator, or alternate base
@@ -761,14 +761,16 @@ virQEMUCapsInitGuest(virCapsPtr caps,
      *  - host & guest arches match
      *  - hostarch is x86_64 and guest arch is i686 (needs -cpu qemu32)
      *  - hostarch is aarch64 and guest arch is armv7l (needs -cpu aarch64=off)
+     *  - hostarch and guestarch are both ppc64*
      */
     native_kvm = (hostarch == guestarch);
     x86_32on64_kvm = (hostarch == VIR_ARCH_X86_64 &&
         guestarch == VIR_ARCH_I686);
     arm_32on64_kvm = (hostarch == VIR_ARCH_AARCH64 &&
         guestarch == VIR_ARCH_ARMV7L);
+    ppc64_kvm = (ARCH_IS_PPC64(hostarch) && ARCH_IS_PPC64(guestarch));
 
-    if (native_kvm || x86_32on64_kvm || arm_32on64_kvm) {
+    if (native_kvm || x86_32on64_kvm || arm_32on64_kvm || ppc64_kvm) {
         const char *kvmbins[] = {
             "/usr/libexec/qemu-kvm", /* RHEL */
             "qemu-kvm", /* Fedora */